Lewis gave up 10 earned runs in 3 1/3 innings against the White Sox on May 22 after he was called up from Triple-A Sacramento.
For the Rivercats, he was 5-1 in eight starts with a 2.31 ERA, moving himself to the front of the line as a candidate to get called up to make a start.
But after that first rough outing, Lewis didn't have to go too far. Instead of going back to Sacramento, he went into the bullpen and has since thrived in that role.
Lewis has appeared six times out of the bullpen, throwing 4 1/3 innings of scoreless baseball, giving the A's a lift at a time when they really needed it, after Huston Street and Justin Duchscherer both went down.
"He's been good, it's something that has definitely helped us," A's manager Bob Geren said of Lewis' move to the 'pen. "I thought that the team would be better off with it that way, and that's been true."
Lewis is no stranger to pitching out of the bullpen, coming up with Texas in 2002 and making 11 relief appearances.
"I played that role a little when I first came up," Lewis said. "I kind of like both roles, but you don't have to think too much pitching in relief as opposed to starting when you have four days off to get ready. When you are in the bullpen and the phone rings, they tell you to get ready for specific hitters."
Before Thursday's game with Boston, Lewis had pitched in 53 games and had started 34 of those games. He made 26 starts with Texas in 2003 and went 10-9.
But Lewis doesn't mind pitching out of the bullpen, and he is happy to be getting an opportunity with a big-league club.
"This is your ultimate goal, to be in the big leagues," Lewis said. "Whether it's in the bullpen or starting is fine with me."
A's ready to cross the Bay: Interleague Play is getting ready to start again and the A's will play their natural National League rivals when they cross the Bay to face the Giants on Friday.
"I like the Bay [Bridge] Series a lot," Geren said. "It's fun playing close to home. I think the fans like it and that's why we are out here."
A's reliever Alan Embree also enjoys the Bay Bridge Series, enjoying it much more than the rest of Interleague Play.
"A series like this is great for the fans," Embree said. "It creates a playoff like buzz."
As for the rest of the Interleague, Embree doesn't necessarily dislike it, but he also isn't the biggest fan.
"I think it's good for the game and good for the fans, but I don't like what it does to our schedule," he said.
Go-go A's: Fans got a glimpse on Wednesday night of the running team that the A's were hoping to be when Spring Training started.
The A's took advantage of Red Sox knuckleballer Tim Wakefield to the tune of four stolen bases.
"I've always felt like our team could run," Geren said. "We will use the running game when we think we can make it."
Mark Ellis, Bobby Crosby, Travis Buck and Shannon Stewart all swiped bags in the 3-2 win.
"I love it," Crosby said of using the running game. "Wakefield is quick to the plate, but it's pretty tough for the catcher to handle that knuckleball."
The last time the A's stole four bases in a game came in May 2001, coincidentally against the Red Sox. That day, it was against starter Tomo Ohka.
Witasick released: After being designated for assignment on Sunday, reliever Jay Witasick was given his outright release Thursday morning.
Witasick was 1-0 with a 3.60 ERA in 16 appearances for the A's this season. He is now able to sign with any team as a free agent.
Lineup shuffle: Mark Kotsay, after getting a scheduled day off on Wednesday night, was back in the lineup for Thursday's afternoon series finale with Boston.
Crosby received a day off and Marco Scutaro was in his place at shortstop. Geren said nothing was wrong with Crosby, but he just wanted to rest him. It will be Crosby's first day off since May 10.
Milton Bradley, who was originally in Wednesday's lineup but was a late scratch, was not in Thursday's lineup. Geren said he hoped Bradley would be ready for Friday's game with the Giants.
Up next: A's righty Chad Gaudin (6-1, 2.41 ERA) will take the ball in the opener of the Bay Bridge Series, opposite Giants righty Tim Lincecum (2-0, 4.05 ERA). The first pitch is set for 7:15 p.m. PT.
Matt Smith is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.