The 36-year-old right-hander held New York to five hits over five innings, leading the A's to a 3-0 series-opening win.
"It's been a long road this year," Tomko said. "It was kind of ironic that my first start here came against the Yankees. ... I had a lot of emotions kicking around before the game."
Those emotions, however, weren't the ones you might expect from a guy facing a team that cut him loose.
"To be honest," Tomko said, "I have no ill feeling toward the Yankees. They have some good guys pitching over there. It worked out well. I'm somewhere where I can get back going."
Yankees outfielder Nick Swisher caught up with his one-time teammate Monday morning before his start.
"He was like, 'Wow, it's just crazy getting that opportunity to face a team you were just with,'" Swisher said. "He did a good job tonight. You've got to tip your cap some nights, and tonight was one of those nights. I know I'm going to get a text message later tonight, no doubt."
Manager Bob Geren said he was hoping for five innings out of Tomko, whose pitch count is being monitored as he stretches from a reliever back into a starter.
Tomko, pitching for his ninth big league team, threw 78 pitches. His previous season high was 55, which came in his last start with Triple-A Sacramento on Wednesday.
"I was hoping for 79 [pitches]," Geren joked.
Tomko got into trouble in the third. Ramiro Pena and Derek Jeter opened the frame with back-to-back singles. After getting Johnny Damon to fly out to right, Tomko walked Mark Teixeira, loading the bases with Alex Rodriguez coming to the plate.
Tomko only needed one pitch, getting Rodriguez to ground into a 1-2-3 double play to end the threat.
A fist pump suggested Tomko was more than a little excited about that.
"I'm not a big fist-pumper," quipped Tomko. "It was exciting. ... It was a make-or-break moment in the game."
"He threw the ball well," Rodriguez said. "We have to do better than that. He gave us good pitches to hit and we missed them."
Tomko wasn't the only one stopping the Yankees. The A's bullpen held them at bay, too.
Craig Breslow retired six of the seven batters he faced, then Brad Ziegler struck out Jorge Posada looking to end the eighth, stranding runners on first and second. Andrew Bailey threw a perfect ninth, earning his 18th save.
"They did a pretty good job," Geren said of the bullpen. "Bailey's been terrific all year, Ziegler did a good job, another multi-inning appearance for Breslow -- they all did well."
Oakland struck for all three runs in the fourth. Rajai Davis got things started, delivering a one-out double. Davis, who extended his career-best hitting streak to 12 games with the knock, then swiped third base. Kurt Suzuki brought him home with a single up the middle against a drawn-in Yankees infield.
Scott Hairston followed Suzuki with a single of his own, then both runners moved up on Ryan Sweeney's groundout to first. A.J. Burnett balked in Suzuki before Mark Ellis plated Hairston with a double to right.
Burnett was the hard-luck loser as he dropped to 10-6. He went the distance, allowing six hits, walking two and striking out five.
Bobby Crosby was lifted in the eighth with tightness in his left calf. Geren didn't have a postgame update on his status.
"He doesn't even know how it happened," Geren said.
Dallas Braden's infected left ankle showed improvement Monday, but he's still a ways away from returning. Geren said he might not be back until September. Tomko will remain in the rotation in Braden's place.