He may not have known it at the time, but on July 10, 2010, Marc Rzepczynski was reinvented.

Two days before the All-Star break, with Blue Jays lefty reliever Scott Downs out nursing a stiff neck, the then-24-year-old Rzepczynski was warming up in the bullpen to face the top of the Red Sox's order.

The left-hander had pitched just three relief appearances during his first Minor League season with Class A Auburn more than three years prior. But with a brief break from pitching ahead during the All-Star break, then-manager Cito Gaston thought Rzepczynski could use some work, bringing him in to protect a three-run lead at the start of the eighth inning.

His relief career didn't exactly get off to a stellar start -- Rzepczynski bounced the fourth pitch he threw off of Red Sox shortstop Marco Scutaro, sending the former Blue Jay to first base.

But Rzepczynski quickly gathered himself, coming back from behind 3-1 to strike out Daniel Nava before sending one of Boston's most feared hitters, David Ortiz, back to the dugout holding his bat on just four pitches, including three sliders that landed for strikes. It was the first time Rzepczynski had entered a Major League game in an inning other than the first and a harbinger of the direction his young career would take.

Now Rzepczynski isn't just filling in for Downs. A former starter now plying his trade from the bullpen as a left-handed reliever, using a fastball, sinker, changeup and breaking ball in late innings, Rzepczynski and Downs are practically synonymous. It's a similarity that has made a believer out of Blue Jays manager John Farrell.

"He's on a very steady pace to become one of the better left-handed relievers in the game," Farrell said of Rzepczynski, who the team converted to a full-time reliever in Spring Training.

That's not just a manager pumping his lone lefty reliever's tires, either. Rzepczynski has allowed just five runs in his 17 1/3 innings this year and went a stretch of 10 consecutive appearances without surrendering a run, allowing just three hits in the span.

He has held left-handed opposition hitters to a paltry .129 batting average (4-for-31). Right-handers don't fare much better, hitting just .222. Rzepczynski has even been effective when pitching from behind in the count, coming back to strike out 10 of the 33 batters he's thrown first-pitch balls to.

But the figure that stands above them all is the fact that of the 65 batters he's faced, just one has mustered an extra-base hit off the southpaw -- Jed Lowrie's double in Tuesday's 7-6 Blue Jays win over the Red Sox.

"We have all the confidence in the world when he comes to the mound. He's been very good for us," Farrell said, noting that Rzepczynski has improved his velocity in 2011, beginning to touch 93 mph on his fastball.

All of this success comes from a pitcher who entered Spring Training competing for the fourth or fifth spot in the Blue Jays' rotation.

A relative veteran on a young pitching staff at 25 years old, Rzepczynski looked to be in good shape, boasting a deep arsenal of pitches. But Toronto had so many candidates for the rotation and lacked a proven left-handed reliever, so Rzepczynski quickly found a niche to fill.

"If the need is there, I'm happy with whatever they have me do. I can't complain," Rzepczynski said. "With all the young starters we have, I know the best role for me is going out there and being that lefty in the bullpen. I want to help the team win."

It's the same path Downs took half a decade ago, when he arrived in Toronto from Montreal, where he had been a starter. The Blue Jays transitioned Downs into a middle-inning reliever, using his experience as a starter to utilize him for two or three innings at a time. Soon Downs became the club's primary setup man, dominating the eighth and posting an ERA of 3.09 or lower in his final four seasons with the Blue Jays. It earned him status as one of the most reliable lefty relievers in the big leagues, a reputation he turned into a three-year, $15 million contract with the Angels this offseason.

Downs' last two seasons in Toronto overlapped Rzepczynski's first two, and the veteran's poise and aggressive philosophy had an effect on the young Californian.

"He wouldn't care what inning it is, if it's a tie ballgame, who he's got out there. He just goes out and attacks," Rzepczynski said of Downs. "He could walk two guys but the next guy is still going to get that sinker down in the zone like, 'Here you go, try and hit it.' I'm trying to do the same thing."

It was Downs who Rzepczynski went to for advice ahead of that first career relief appearance against Boston. Rzepczynski has bought a fearless approach when he comes out of the 'pen -- a gamble that has paid dividends.

"Hey, you know what you're getting when you face me. You know you're going to get a sinker," Rzepczynski said. "It's the same thing. 'Here it is -- go hit it.'"

That kind of all-in approach is right in line with what Blue Jays bullpen coach and former American League Cy Young Award winner Pat Hentgen has been preaching to his young lefty.

Hentgen himself was utilized as a reliever by the Blue Jays in his first two years with the club after pitching as a starter throughout his time in the Minors. Then 22, Hentgen saw middle-inning work during the Blue Jays' 1992 World Series season, posting a 5.36 ERA. His first Major League win came in relief on April 10, 1992, against the Orioles, pitching scoreless eighth and ninth innings, which allowed Roberto Alomar to win the game with a walk-off single.

While Hentgen was eventually reverted back to a starter -- he led the Majors in complete games and shutouts twice -- he did pick up a thing or two about the transition from starting to relief, which he's tried to relay to Rzepczynski.

"We always talk about it -- the organization's been asking you to get 20 outs for the last four or five years, and now you need to just get three. So let's just attack and go at people," Hentgen said.

It's a simple creed -- if nothing else, throw strikes.

One of the biggest hurdles for starters making the transition to the bullpen is their pitch sequence and how important it is to avoid nibbling in relief. Many starters will only show a batter a couple of their pitches in the early going, working around the zone and saving an out pitch for later in the game when the batter comes up again.

But Hentgen and Farrell have both stressed to Rzepczynski the need to attack the strike zone right from the get-go with his fastball and sinker. It's a lesson that has not been lost on the young southpaw.

"I give them the best of what I've got -- I'm not trying to set them up for the second and third time facing them," Rzepczynski said of facing batters in relief. "Get your two best pitches going and just attack from pitch one. That's the plan."

Rzepczynski doesn't bother playing coy with hitters, throwing over 60 percent of his pitches this season for strikes.

That's helped him strike out more than a batter an inning, using his sweeping slider to miss bats. But more than anything, it's been his sinker that has induced ground balls for exactly half of his outs on the season. Even right-handed batters can't find much success against Rzepczynski as he works his changeup and breaking ball to them on both sides of the plate.

"For righties, the changeup is a huge pitch. That's the thing I've been working on for two years," Rzepczynski said. "I think it's a great pitch."

Rzepczynski's experience as a starter has also blessed him with above-average endurance, meaning Farrell has had little hesitation in using his only left-hander on back-to-back days. He trails only long reliever Carlos Villanueva and workhorse Shawn Camp in the bullpen with 17 1/3 innings pitched and has made a team-leading 18 appearances.

That may seem like a lot for Rzepczynski's first year pitching out of the bullpen, but Hentgen feels he may even be underused.

"I think he could throw three, four days in a row, to be honest," Hentgen said. "I think that he's already proven [his endurance] in his short career. It's just a matter of staying healthy and getting his work in. He could have a very long career."

And while Rzepczynski runs the risk of being labeled a left-handed specialist, both Farrell and Hentgen were adamant that there is little trepidation in leaving the southpaw in to face right-handers.

"There's no debate. Nobody even thinks about bringing him out to face the righty. He's very effective to both sides of the plate," Hentgen said.

Which sounds an awful lot like Downs. And while the door is certainly still open for Rzepczynski to return to starting, there won't be even a shade of disappointment if his career treads a similar path to Downs'.

"He's made a hell of a career being a reliever. He's probably one of the top lefty bullpen guys, and he's been throwing the same stuff for six, seven years," Rzepczynski said of Downs. "If I end up being anything like him, when I finally hang up my cleats, I definitely won't have any complaints about my career."