The 33-year-old Sexson batted .218 with 11 home runs and 30 RBIs in 74 games for the Mariners, posting a .315 on-base percentage before being released on July 10. Sexson will be in the lineup Friday when the Yankees meet A's starter Greg Smith, a left-hander.
"I'm just pretending like it's the start of a new season," Sexson said. "Coming into a clubhouse like this makes it a lot easier too. You've got a lot of guys that do a lot of good things in this clubhouse. You can just hopefully try to add to something that's pretty much put together."
He batted .344 with five home runs in 61 at-bats against lefties for the Mariners before his release on July 10, clearing waivers to become a free agent. Sexson said that he had other offers but decided, "This was the right place for me. It's somewhere that I've always wanted to play."
A first baseman by trade, Sexson is expected to help complement Jason Giambi in the Yankees' infield, with the right-handed-hitting Sexson playing against left-handed starting pitching. He could also see time as a designated hitter.
"Obviously, the better you play, the more you play," Yankees manager Joe Girardi said. "He's going to start [Friday] and we'll just take it day by day. Richie is a guy that has big power and has played good defense and driven in runs in his career. We just want to get him back to where he was and have him produce for us."
The Yankees officially announced the completion of Sexson's contract on Friday, optioning left-hander Billy Traber to Triple-A Scranton/Wilkes-Barre and transferring right-hander Phil Hughes to the 60-day disabled list in corresponding moves.
Sexson has not played since July 8 at Oakland, but worked out with the Yankees on Friday afternoon and said that he did not feel rusty.
"I sat back and thought about things," Sexson said. "This is a place that I was hoping would call, because it's where I wanted to play. I'm glad to be here and you never know if [the time off] can help you or not."
The Yankees have tried a variety of combinations at first base this season. Giambi has impressed by remaining healthy and on the field for most of the campaign, but New York has been unable to find a right-handed complement.
Shelley Duncan was optioned to Triple-A Scranton/Wilkes-Barre and is now thought to be out for the season after separating his right shoulder while diving for a ball, and Morgan Ensberg was designated for assignment on June 1 after making the team with a $1.75 million contract out of Spring Training.
Most recently, the Yankees had been sprinkling in starts for Wilson Betemit at first base. Sexson's addition likely returns Betemit to reserve infield duties.
"[Sexson is] the type of guy that can change the game with one swing," Girardi said.
A two-time American League All-Star (2002 and '03), the 6-foot-8 Sexson has a career batting average of .261 with 305 home runs and 937 RBIs over 12 Major League seasons with the Cleveland Indians, Milwaukee Brewers, Arizona Diamondbacks and the Mariners, with whom he signed a four-year, $50 million contract before the 2005 season.
The Mariners will pick up most of the $14 million Sexson is due this year. The Yankees will be responsible to pay only Sexson's pro-rated minimum Major League salary. Sexson said that he was trying to stay away from the subject of what transpired in Seattle.
"We just underperformed," Sexson said. "I think everybody did. I feel bad that we cost some people their jobs, and the axe has to drop down on somebody. It just happened to be the manager, general manager and a couple of players. We just underperformed as players, plain and simple."
Yankees general manager Brian Cashman had admitted the club's interest in Sexson recently, with the franchise in need of an additional power bat due to Hideki Matsui's lingering injury troubles. At the same time, Cashman downplayed any potential interest New York would have in signing Barry Bonds, also a free agent.
Matsui is feared lost for the season after experiencing increased left knee inflammation. Matsui has had the problematic knee drained twice already and cut short a rehabilitation assignment in Tampa, Fla. He is scheduled to be examined by Yankees team physician Dr. Stuart Hershon on Friday.
Matsui had arthroscopic surgery on his right knee after the 2007 season and Cashman said recently that he was "not optimistic" that Matsui would be able to avoid a similar fate this year. If Matsui were to have the procedure now, it would cost him the remainder of the campaign.
The Yankees are also without Johnny Damon, who went on the 15-day disabled list after bruising his left shoulder in a July 4 game at Yankee Stadium and experienced a mild setback that pushed his target date of active duty to late next week. Damon was to meet the Yankees in New York on Friday and continue his workouts during the homestand.
Bryan Hoch is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.