MINNEAPOLIS -- The Twins have made additions over the winter to boost their starting lineup, but the pitcher who could perhaps have the biggest impact on their rotation is one that's already familiar to Twins fans -- Francisco Liriano.

Liriano is coming off his worst season with the Twins, having gone 5-13 with a 5.80 ERA in 2009, but the left-hander has bounced back this winter while pitching for Leones del Escogido in the Dominican Winter Leagues. He helped the club earn a postseason berth and then went 3-1 with a 0.49 ERA in seven playoff starts, while recording 47 strikeouts and five walks in 37 innings.

It's the type of performance that has the Twins cautiously optimistic of what Liriano could bring to the club in 2010.

"He could be our ace in the hole," Twins manager Ron Gardenhire said this weekend during the club's annual fan festival, TwinsFest. "We said a few years ago that this guy is potentially a No. 1 [starter]. Everybody is always looking for No. 1 guys. I don't want to put pressure on him and say he's a No. 1 guy. But he's had No. 1 stuff and he's had No. 1 success before. You never know what's going to happen but it could be very entertaining."

The Twins have four starters already penciled into their rotation for 2010 -- Scott Baker, Nick Blackburn, Carl Pavano and Kevin Slowey. Liriano is expected to compete for the fifth and final spot in that rotation but it's likely to be a heated battle with Brian Duensing and Glen Perkins also in the mix.

Still, there seems to be no better time for Liriano to be in such a competition, based on how he is now feeling.

"I've got my confidence back," Liriano said. "This winter is the best I've felt."

Liriano finished off his tremendous run in winter ball as the winning pitcher for Leones del Escogido in the Domincan Winter League championship game on Thursday night. He pitched five scoreless innings, striking out 10 while allowing one hit, to defeat Gigantes del Cibao -- the club of his current Twins teammate, Alexi Casilla.

"He killed me," Casilla said with a laugh when asked about Liriano's winter performance in the Dominican. "He kill everyone."

The reports out of winter ball were that Liriano's velocity had gone up, with his fastball topping out at 95-96 mph on the radar gun and his slider in the high 80s. While Liriano's radar readings in the Dominican have at times been skewed, the pitcher said he's noticed a significant difference in the way he's throwing.

"I'm throwing a little harder now and I've got better control," Liriano said. "I'm locating my fastball better. My slider is way better too. The first year coming back from my surgery, my arm didn't hurt at all but I didn't have the power in it. Now I feel stronger than before."

During TwinsFest this weekend, Liriano's performance in winter ball was a common topic of conversation. The impressive numbers from the left-hander have not only caught the attention of the Twins front office and coaching staff, but also his teammates.

"For him it seems a lot goes back to confidence," said first baseman Justin Morneau. "Last year I don't think he felt like he could repeat his delivery like he wanted to and he didn't have the control he wanted to. If he gets that and gets his confidence going, he might be that true No. 1 that every team needs. If he can get close to where he was, it will be fun to watch."

The question surrounding Liriano has always been whether or not he can regain the form that he had during his breakout rookie season in 2006. That was when he was the talk of baseball, posting a 12-3 and a 2.16 ERA before his year was cut short by an elbow injury, which eventually required Tommy John ligament replacement surgery.

Heading into the '09 season, the Twins were optimistic that Liriano was on track to being at least an effective starter. The pitcher had gone 6-1 with a 2.74 ERA in 11 starts over the final two months of the 2008 season. But instead they watched him regress in '09, his first full season in the Majors following surgery, and his problems seemed as much mental as anything.

That's why this recent performance in winter ball has everyone excited, including Liriano.

"[It was like], this is me," Liriano said of the way he was throwing. "That's the way I know how to pitch. Not worry about anything or any hitter. Just go out there and try to throw first pitch strikes and locate my fastball. I feel like I did in '06, I have my confidence back. My arm feels great. Physically and mentally I'm ready to go.

Liriano also was displaying a trimmer physique at TwinsFest. He said that he's lost some weight since the end of last season by placing more of a focus on his physical conditioning -- including running more often. The Twins have taken notice of the changes and are pleased by what they've seen.

"I think Francisco realizes this is a big year for him," Twins general manager Bill Smith said. "And this is a big year for him."

Liriano will head to Spring Training in the mix for a starting job, but he'll also be an option for the bullpen if he doesn't earn the fifth spot in the rotation. His preference of course is to be a starter and so for now Liriano is focused on proving to the Twins that last season's struggles were just a fluke.

"I am going to go out there and show them I'm ready," Liriano said. "And hopefully [that means] I can be in the starting rotation."