Saunders pitched fairly well himself, holding the Yankees to seven hits and three runs over 6 1/3 innings, but knew he was in a tough battle as Pettitte zipped through his work while allowing baserunners in only the fourth inning until a leadoff single in the eighth.
"I was watching him get up and get down pretty quick today," said Saunders. "That makes it kind of good in a way, but bad because you know he's throwing up zeros. I'm struggling out there throwing 20-30 pitches an inning, and next thing you know there's two outs already and I haven't even had a chance to [go to the bathroom]. Tip your cap. He was great today."
Saunders was pretty good also, with his second run coming only after a defensive gaffe that didn't count as an error but did allow the Yankees to take the lead in the fifth. Saunders' final tally came after reliever Danny Farquhar replaced him in the seventh and couldn't strand an inherited runner.
It was just the second loss in 16 career starts at Safeco for Saunders, who is now 10-2 with a 2.31 ERA lifetime at the park and 4-2 with a 2.53 ERA in seven starts this year while with the Mariners. That stands in stark contrast to his 0-4 record and 9.00 ERA in six road starts this year.
"Joe threw the ball really well," said Mariners manager Eric Wedge. "He's starting to kind of lock it in and get into a groove. He has a much better feel for himself now in regard to what he wants to do. He's been pitching for a while, and you're seeing what we'd hoped we'd see and more consistency with Joe."
The loss dropped Seattle to 27-36 on the season and 2-4 on the current homestand going into Sunday's series finale with the Yankees, who improved to 36-26.
After the Mariners struggled dealing with Pettitte, 43-year-old Mariano Rivera came in to notch his 630th career save and 36th in 38 chances against Seattle.
"Pettitte did a nice job," said Wedge. "We tried to make some adjustments and he adjusted right back. Very efficient. He's amazing. There are a couple guys over there that have had amazing careers and are still doing it at the highest level."
Mariners rookie second baseman Nick Franklin singled in his third at-bat against Pettitte for one of Seattle's four hits on the day, but then struck out against Rivera with two on and two outs in the ninth.
"It's a learning process," Franklin said. "More than anything, it's just good to see these guys and get a feel for them because it's just going to make you that much better."
Saunders gave up a run in the first on Robinson Cano's single to right field after Mark Teixeira had doubled with two outs, but the lefty shut down the Yankees for the next four frames until the visitors took advantage of a fielding miscue.
After a walk and a one-out single, Saunders appeared out of the fifth after inducing Brett Gardner to hit an apparent double-play grounder to third. But Franklin dropped the ball on the transfer after taking Kyle Seager's throw, and that left the door open for Jayson Nix to deliver an RBI single that made it 2-1.
"It was a slow ground ball and I knew Gardner was a pretty fast runner, so it was a do-or-die," Franklin said. "I knew I had to get rid of it and not take very long because he was going to beat it out."
The Yankees scored again in the seventh when Gardner's one-out double knocked out Saunders after 106 pitches. Nix greeted Farquhar with an RBI single that counted as Saunders' third run.
Seattle didn't touch Pettitte until a leadoff single by Jason Bay in the fourth, and he eventually scored on a sacrifice fly by Michael Morse.
That turned out to be the only inning in which Pettitte allowed a baserunner until Franklin's leadoff single in the eighth. The 40-year-old southpaw gave up just three hits with no walks and six strikeouts in 7 1/3 innings in improving to 5-3 with a 3.82 ERA on the season.
Pettitte is 12-13 in 26 career starts against the Mariners, who remain the only American League team against which he owns a sub-.500 record.
Brandon Bantz made his first career start for the Mariners at catcher, going 0-for-2 before being pinch-hit for in the eighth. Bantz received a standing ovation from the crowd before his first at-bat, with home-plate umpire Laz Diaz telling him to tip his cap before getting into the box.
"That was something I didn't really expect at all," said Bantz, called up this week when Jesus Sucre injured his left hand. "I got some chills through my body there. I didn't really know what to do. Do I wait, do I let them keep going, do I step in here? Then Laz looks at me and said, 'You're not stepping into the box until you give them a wave.' That was a moment I'll never forget, the Mariners faithful there. I appreciate that a lot. That was pretty cool."
Seager extended his hitting streak to 12 games with a 2-for-4 day, but first baseman Kendrys Morales went 0-for-2 before being removed in the sixth with back stiffness.