OAKLAND, Calif. (AP) -- Jon Lester walked through the Oakland clubhouse doors to quite a greeting, from the snappy, patriotic marching tune blaring from the sound system to the handshakes and hellos from every corner.
And even the familiar friendly face of his former pitching coach in Boston, Curt Young.
Lester arrived with fanfare Friday to join baseball's winningest team: the small-budget Oakland Athletics, who are counting on him to be an instant ace on a rotation full of No. 1 starters.
''Obviously leaving Boston after being there for so long is at times difficult, but to be going from a team that hasn't done so well this year to a team with best record in baseball is pretty exciting,'' he said. ''Fortunately I've got a few faces here that I recognize and know pretty well, so it should make the transition pretty smooth.''
The All-Star left-hander (10-7) will make his A's debut Saturday afternoon at the Coliseum against Kansas City, pitching on seven days' rest. He is 4-0 with a 1.07 ERA over his last eight outings.
For Lester, just knowing where he will be for the remainder of the season was comforting a day after being traded along with outfielder Jonny Gomes to the two-time reigning AL West champions for outfielder Yoenis Cespedes. On Saturday, 10,000 Cespedes T-shirts will still be distributed.
''I'm a marketing department's worst nightmare,'' A's general manager Billy Beane said.
Lester is committed to doing his part every fifth day for a franchise poised for another October playoff run if things keep going this well over the season's final two months.
''Kind of the anxiety of it, not really knowing where you're going to be and having a family makes it difficult,'' Lester said. ''To leave someplace I've called home for eight years that made it a little bit hard, but like I said, I'm happy to be here and happy to be a part of this and hope to contribute.''
While Lester and Young already know each other well, Gomes' presence should help Lester adjust, too. The outfielder was a fan favorite in 2012 as the A's stunned the Texas Rangers on the season's final day to grab the division crown and end a five-year playoff drought.
An A's team Lester praises for being ''full of energy, they play the game the right way,'' is hardly one he considers to be in need of much help the way this season has gone so far in a much-improved AL West.
Yet Oakland's brass - and the players, too - believe the addition of Lester gives them an edge to not only make sure the A's reach the playoffs but to give them the best chance of advancing following consecutive five-game division series defeats to the Detroit Tigers.
''Not only is this guy well decorated in climbing the totem pole of left-handers in the game and left-handers in the postseason in the game,'' Gomes said. ''You guys don't get to see the work ethic, what goes into goes into his success, what goes into his championship pedigree, something I didn't know on the other side. It truly is a breath of fresh air to know the best pitcher on the team is also the hardest working guy on the team.''
Lester plans to complement what already is working so well.
''These guys have been in the playoffs before, they've made runs before,'' he said. ''It's not going to be anything new for a lot of these here. Hopefully with adding us we can maybe add a little more experience and on the further side of it, going deeper.
''I wouldn't consider it pressure. These guys expect to go to the playoffs every year now. It's a good atmosphere to have.''
Gomes doesn't want to alter the chemistry the A's already have, though he fit right back in as if he'd never left, saying, ''I'm not here to mix things up.''
Same goes for outfielder Sam Fuld, who rejoined the A's following his trade from Minnesota just four months after starting the year in Oakland.
Lester has no idea what's next beyond the 2014 season as his contract is due to expire - and he still isn't ruling out a return to the Red Sox down the road.
''Any time you negotiate with a team and it doesn't go the way everybody wants, I think there's always going to be disappointment,'' Lester said. ''That's not to say the effort wasn't there on both sides to try to get something done. But my time in Boston is something that I'll always remember, always cherish, from 2002 to yesterday. Nothing but great things to say about the organization, the way they treated me, the way they treated my family through the good times and the bad times. They were always consistent. I thanked them personally yesterday for everything they've done. We'll see where that relationship goes later on. Right now, I'm an 'A.'''