The Twins moved Liriano from the rotation to the bullpen and sent Valencia, once a promising third base prospect, to Triple-A Rochester as part of a major shakeup to try and instill some energy and life into a team that has shown very little of either through the first 30 games.
The moves were made after another lackluster performance in a 6-2 loss to the Los Angeles Angels on Wednesday night.
"We need to make some changes," Twins manager Ron Gardenhire said. "We need some hits. We need some new life in here, the whole package."
Josh Willingham hit his sixth homer of the season, but Carl Pavano (2-3) was knocked out of the game before there was an out in the fifth inning. He gave up five runs -- four earned -- and 10 hits in his shortest outing of the season.
Ervin Santana (1-6) gave up two runs and six hits in 7 1-3 innings for the Angels, getting some run support for the first time in six starts.
The Twins entered the season desperately needing Liriano to assert himself at the top of the rotation and Valencia to give them some power at third base.
But Liriano is 0-5 with a 9.45 ERA in six starts in the final season before he is set to become a free agent. Gardenhire said the team still wants him in the starting rotation, and hopes that the move to the pen will help him regain some of his lost confidence.
"Maybe a couple innings here, a couple innings there, he blows some people away and gets some kind of mojo going," Gardenhire said. "Then we see if we can get him back in there. We need him as a starter. We told him that. He has the best arm on this team and we need to get him some confidence going, get some quality innings out of him, maybe help us win a few ballgames out of the bullpen right now. Eventually we're going to need him as a starter."
Liriano left the clubhouse before the Twins announced the news, but Gardenhire said the lefty took the move in stride.
"Frankie said, `Whatever you need me to do," Gardenhire said. "He made sure that he told Andy and I that he understood, and that he's not upset about it, and he wants to help the baseball team any way he can."
In the meantime, the Twins selected the contract of right-hander P.J. Walters from Rochester. Walters is 3-1 with a 2.70 ERA in six starts for the Red Wings this season. He will start on Saturday against Toronto.
Valencia is hitting .190 with one homer and 11 RBIs. He went 0 for 4 on Wednesday night and said the news didn't come as a surprise. The 27-year-old Valencia has improved defensively this season, but is slugging just .290 with a .204 on-base percentage.
"Obviously nobody wants to get sent down, but it's hard not to say I didn't see it coming because I haven't been hitting very well," Valencia said. "I've been inconsistent. My defense has been good, but I'm a guy that needs to contribute offensively. He's right, they're right. I just have to go down there and work hard."
Mastroianni hit just .143 at Double-A New Britain before being promoted to Triple-A, but he hit .346 with two doubles, two triples and 11 RBIs in 19 games for the Red Wings.
"Mastroianni's been playing the living fire out of the game down there," Gardenhire said. "They told me he's the most exciting player down there."