Felix Hernandez has been as dominant on the mound as anyone in the American League, leading the Junior Circuit with his 2.34 ERA and 153 2/3 innings.
The Red Sox's lineup, meanwhile, has been as tough as any in baseball, sitting top-two in the Majors in runs, batting average and OPS.
Something will have to give on Thursday night at Fenway Park when the two clubs clash in the finale of a three-game set. Following a 5-4, 15-inning win early Thursday morning, the Red Sox will go for a three-game sweep.
But standing in their way will be Hernandez, who's riding a hot streak that dates back to late May. He hasn't lost since May 25 and is 7-0 with a 2.18 ERA over that time.
The right-hander threw nine innings of one-run ball in his most recent start -- a no-decision against the Twins on Friday.
"It was vintage Felix," said acting manager Robby Thompson. "But obviously we didn't have a lot of run support for him, and we squandered some opportunities. But Felix was Felix."
Hernandez faces a Boston club riding the high of acquiring one of the trade market's top arms in Jake Peavy. Earlier this month, the Red Sox acquired reliever Matt Thornton from the White Sox, too.
"We thought we had a good team, and, you know, we were fine with what we had," Boston first baseman Mike Napoli said. "But the front office made us better."
Right-hander Ryan Dempster gets the ball for the Red Sox after he tossed 5 1/3 solid frames to pick up the victory over Baltimore on Saturday. The Mariners pounded Dempster for seven runs on nine hits in 3 1/3 innings on July 11 in Seattle, but Boston rallied to win, 8-7.
The Red Sox, who moved into first place with Wednesday's extra-inning victory, have won five straight games against the Mariners. That's their longest streak against Seattle since taking 10 in a row during the 1991 and '92 seasons.
Mariners: Quiet at the Deadline
Seattle general manager Jack Zduriencik was active with the phones in the days leading up to Wednesday's Trade Deadline, but the Mariners opted not to reshuffle their roster.
"There were discussions," Zduriencik said. "But at the end, I didn't think there was the right situation for us at this time. There's an obligation here to our fans and certainly to the players here on this team. They've played well recently."
Veterans Kendrys Morales, Raul Ibanez and Oliver Perez were all potential targets for other clubs.
Red Sox: Players abuzz about Peavy
The addition of Peavy at the Trade Deadline was a move endorsed emphatically by the players in Boston's clubhouse.
"He's a guy that goes out there every day, and he's reliable and gives you everything he's got," said catcher Jarrod Saltalamacchia. "You know that's big. We're in a tight race right now, and we've got two big months coming up, so all the help is better."
Peavy, who won the National League Cy Young Award in 2007 with San Diego, was 8-4 with a 4.28 ERA in 13 starts this year for the White Sox.
• Hernandez has held Napoli to a .167 batting average in 36 at-bats. David Ortiz, meanwhile, is hitting .310 with a .429 on-base percentage against the right-hander.
• Boston's 225-163 record against Seattle is the best record for any club against the Mariners.
• Mariners third baseman Kyle Seager hit .396 (38-for-96) in July.