Pettitte was back on the mound Sunday for the Yankees, getting lavished with adoration while pitching into the seventh inning despite giving up a pair of two-run homers in New York’s 6-2 loss to the Seattle Mariners.

It was as if he never left.

“I just cannot believe how comfortable this is for me,’’ Pettitte said. “I don’t know how to explain it.’’

Nearly lost amid the excitement over Pettitte’s first major league appearance since retiring after the 2010 season was party crasher Kevin Millwood’s performance for Seattle. Millwood (1-4) gave up three hits in seven innings and got his 2,000th career strikeout as Seattle avoided a three-game sweep.

The Yankees tried to prevent their old pal Pettitte from taking the loss with a rally in the eighth against four Seattle relievers. Robinson Cano was walked with two outs by Charlie Furbush with the bases loaded to make it 4-2. Mark Teixeira, though, struck out to end the inning.

The lovefest for Pettitte (0-1) began when the lefthander appeared with several players in videos welcoming fans to Yankee Stadium after batting practice. The cheers grew as he strolled to the bullpen for warm-ups and fans rose for a standing ovation when the five-time World Series champion went to the mound for the first inning.

“I thought it was so awesome. I was so excited. I know we lost today and that’s what a lot of people are going to focus on - I could really care less about that,’’ Yankees outfielder Nick Swisher said. “We got our boy back.’’

Pettitte even got special treatment from the Bleacher Creatures. They broke protocol after their roll call and started a chant for Pettitte that most of the 41,631 in attendance joined in on. The Creatures normally don’t include the starting pitcher when calling out players’ names in the first inning.

Yankee Stadium got awful quiet, though, when Casper Wells homered in the sixth to give Seattle a 4-1 lead with his first of the season, an opposite-field drive off the netting on the right-field pole. Justin Smoak homered for Seattle’s first hit with two outs in the fourth.

Pettitte’s return had become more important to the Yankees because their rotation had been struggling. But through the first five games of this homestand, the starters were 4-0 with a 1.31 ERA and manager Joe Girardi thought their performance would take some of the pressure off Pettitte.

Pettitte, 39, appeared calm as ever in his first big league start in 573 days, since Game 3 of the ALCS against Texas on Oct. 18, 2010. He sat out last season before deciding in mid-March to make a comeback.

With his cap pulled low, and peering over his glove held up in front of his nose, it looked as if No. 46 never left New York.

“To me it looked like he hadn’t missed a beat,’’ Girardi said.

Said Pettitte, “There is not a question in my mind how this is going to play out for me. It’s not about this one start. I’ll measure if this was a successful return or not at the end of October.’’