Also not so long ago, Reds right-hander Homer Bailey, who faces the Twins on Friday in the opening game of a three-game Interleague series at Great American Ball Park, was considered on his way to becoming one of the next big things in baseball.
Things have changed, but each of the three stars still has hopes of getting back to where they were in their careers, or in Bailey's case, where many expect him to be.
Mauer batted .347, .293, .328 and .365 from the 2006 to 2009 seasons and was the American League MVP in 2009, when he also hit 28 home runs and had 96 RBIs.
In the same stretch, Morneau had seasons of 34, 31, 23 and 30 homers and RBI totals of 130, 111, 129 and 100.
He was the AL MVP in the Twins' division-winning 2006 season.
Assorted injuries have bedeviled the two Twins stars in recent years, and both still are struggling to regain their former All-Star form.
Mauer has played in 60 games this season and is hitting .314, but with just three home runs and 33 RBIs. He was held out of the lineup in the Twins' three-game series with the Pirates, and there's a chance he could return for this weekend's series with Cincinnati.
Mauer suffered a bruised quad in a home-plate collision with Milwaukee's Rickie Weeks on Sunday.
"The biggest thing right now is that it swelled up pretty good, so I'm fighting that," Mauer said. "I'm trying to get the swelling down. So hopefully I can get it down to a spot where I can run a little bit."
Morneau has appeared in 51 games this season and is hitting .241 with 10 home runs and 33 RBIs.
Morneau's numbers against right-handed pitchers this season have been in line with his career numbers, but he's struggled against left-handers. Entering play Thursday, Morneau was hitting .318 with eight homers against right-handers. But against lefties, Morneau was batting just .091 with two homers and 20 strikeouts.
"I think he's definitely pressing a little bit when he gets up there," Twins manager Ron Gardenhire said. "I think he's thinking about it an awful lot and thinking about what's going wrong instead of seeing it and hitting it."
Gardenhire also talked about the importance of having both Mauer and Morneau in the lineup together.
"It's great having these guys batting 3-4, 3-5. Just those two big guys in there is huge for this baseball team. You build your team around those two guys. When they're in the lineup they give you that opportunity because they've proven they know how to win baseball games. They know what it takes. Having them on the field is huge. And you definitely feel it when you miss one or the other."
Bailey is 30-27 in his Major League career, which began in 2007 with the Reds.
This season, he is 5-4 with a 4.03 ERA in 13 starts and is coming off a good performance Saturday in a 4-1 win against the Mets, going eight innings and giving up one run on six hits.
Reds manager Dusty Baker said Bailey kept the Reds in the game in the early innings.
"Homer was outstanding," Baker said. "He got out of trouble like the first three out of four innings. He made some quality pitches, his pitch count remained relatively low. ... He was dealing tonight."
Bailey felt good about his performance.
"I don't know if it's physical effort, but you try to get locked in a little more and try to make good pitches, but also try not to do too much," Bailey said. "We were able to get out of a jam in the second, and then from then on we just kind of cruised along."
Twins: Blackburn gets the start
Bailey's mound opponent will be right-hander Nick Blackburn, who has battled injuries and struggled to a 3-4 record with a 7.48 ERA in 10 starts. In his last start Sunday against the Brewers, Blackburn pitched six innings and gave up nine hits and four earned runs in a game the Twins eventually won, 5-4, in 15 innings.
Reds: Arroyo loss snaps streak
When Bronson Arroyo was roughed up for eight hits and five runs in four innings during Wednesday's 8-1 loss to the Indians, he was charged with the first loss by a Reds starting pitcher since June 5.
Twins closer Matt Capps threw before Wednesday's game against the Pirates, and his status was uncertain for Thursday's finale or the series against the Reds.
Capps, who is dealing with inflammation in his right shoulder, hasn't pitched since allowing a two-run homer in Minnesota's 5-3 loss to Milwaukee on Friday.