In five starts this season, Morales is 2-1 with a 3.42 ERA. He probably won't be a mainstay in the rotation when Beckett returns, tentatively on Wednesday.
Nonetheless, manager Bobby Valentine knows Morales is capable of tossing a strong outing.
"He's pitched very well for us every time he's been on the mound as a starter or a reliever, not every time but the majority of the time," Valentine said. "I'm expecting him to be healthy, sound, aggressive, pound the strike zone, use his three pitches and help us win a game."
The Red Sox have lost four in a row after Joe Mauer's three-run homer in the ninth helped the Twins take a 6-4 comeback victory.
"Talent can only go so far. You have to figure out ways to win," outfielder Cody Ross said. "There's a difference between being a really talented group and being a winning group. On paper it looks like that, but right now it just feels like we're treading water. It's not a good feeling. We have to snap out of it."
The Twins will counter with right-hander Nick Blackburn, who's coming off his best start of the season. He went eight innings against the White Sox, giving up two runs on five hits and throwing a season-high 106 pitches.
"It's the best I've felt in a long time," Blackburn said. "I was finally out there relaxing a little bit and letting the ball move around."
He said he relied heavily on a sinker and that the pitch will be a big part of his plan going forward. Blackburn's ERA is below 7.44 for the first time since May 11.
The Twins won three straight games at Fenway Park for the first time since they won five in a row from Sept. 25, 1993, to June 15, 1994.
Red Sox: Three-catcher rotation may not be permanent
The Red Sox called up Ryan Lavarnway from Triple-A Pawtucket on Wednesday, adding another catcher to a roster that already had catchers Kelly Shoppach and Jarrod Saltalamacchia.
Valentine isn't quite comfortable with carrying more than two catchers.
"It's nothing I've ever been comfortable with or tried to do, I don't think," Valentine said before Saturday's game. "But if they're here the whole time I will get them work behind the plate."
Over the past four days, Valentine has started Shoppach twice and Lavarnway and Saltalamacchia once. Shoppach got the start on Saturday for the second straight day.
When David Ortiz returns from the disabled list next week, the Red Sox will probably remove a catcher from the roster.
Twins: Willingham likely back in the lineup Sunday
Josh Willingham, out of the starting lineup on Saturday against the Red Sox, will probably start in Sunday's series finale. Twins manager Ron Gardenhire wanted to give the left fielder a day off because Willingham leads the team in games played with 103.
Willingham served as designated hitter in the first two games of the series.
"He plays every day, every inning," Gardenhire said. "Even DH is not a break. He's still got to physically to go out there and play baseball every day. I told him let's just go out there and take a day. He's happy with it. I think he knows he needs a break every once in a while. He can't play them all."
Willingham pinch-hit in the eighth inning on Saturday and grounded into a fielder's choice. He is batting .263 on the season with 27 homers and 80 RBIs.
Right fielder Ben Revere singled three times on Saturday to extend his hitting streak to 18 games. It's the longest Twins hitting streak this season.
The Red Sox are 31-42 against right-handed starters and 22-13 against lefties.