Batting ninth in the lineup, Blanco sent an 0-2 pitch into the left-field seats to erase a 2-1 deficit. The 16-year veteran was playing in his 32nd game of the season, the 17th with Seattle after being signed as a free agent.
"If we could get that by the backup catcher every other day, every third day, we'll be in good shape," acting manager Robby Thompson said. "He comes to play, he's in great shape."
Blanco has played for 11 different teams during a career that began in 1997. This was his third homer of the season; the other two were grand slams, including a game winner in his Mariners debut against Oakland on June 15.
"When you get a win and you can help the team win some games, it's a good feeling," Blanco said.
Blanco's batting .182, but he's done his job quite capably.
"He's had some huge hits for us," Thompson said. "Huge home runs, a couple grand slams and a two-run there. The times that he's in there, he's produced."
Blanco isn't the only old-timer in the Seattle clubhouse. The Mariners' other run Sunday came from 41-year-old Raul Ibanez, who hit an RBI double in the second inning.
"That's a good thing," Blanco said. "At this point, you just want to contribute to win games and hope for the best. Raul is a pretty good hitter, he's always been, and I just get lucky."
Saunders (10-10) worked out of trouble in almost every inning but improved to 7-0 lifetime against Baltimore after allowing two runs, eight hits and two walks in six innings.
He walked off the mound for the last time trailing 2-1, but Blanco's blast made him a winner.
"It was unreal," Saunders said. "It's one of those moments in the game where it's like do or die and he put a good swing on a good pitch, I think, and bailed me out."
Saunders, who played a key role for the Orioles late last season, has five consecutive seasons with at least 10 wins. In this one, he walked a tightrope through five innings and gave up a two-run drive to Danny Valencia in the sixth.
Baltimore went 0 for 11 with runners in scoring position and stranded eight. The Orioles dropped two of three to the Mariners and went 4-5 on a homestand that began with three games apiece against Boston and Houston.
"We did some really good things to create some situations, but Joe pitched out of it," manager Buck Showalter said. "It was really kind of characteristic of a good veteran pitcher like Joe. We've seen that before."
Yoervis Medina struck out four in two perfect innings and Danny Farquhar got three straight outs for his second save, both of which came within 24 hours.
Chen (6-4) gave up three runs and five hits over seven innings in losing for the first time in seven starts since May 1.
Valencia was recalled from Triple-A Norfolk before the game for his third stint with the Orioles this season. Starting at designated hitter, he homered after Steve Pearce drew a leadoff walk to put Baltimore up 2-1.
The lead didn't last. One inning later, following a walk to No. 8 hitter Brendan Ryan, Blanco pulled a slider a few feet inside the foul pole.
"That's the spot I wanted to attack," Chen said through an interpreter. "I threw the ball right on the spot and he still swings the bat really well and he hit a home run off me. Hat's off to him."
Seattle and Baltimore combined for 14 homers in the three games, none more important than Blanco's.
"I wasn't expecting to hit a home run," Blanco said. "I was trying to get a pitch where I could put the ball in play and see if something can happen. I just hit it pretty good."
The Mariners used successive doubles by Michael Morse and Ibanez to go up 1-0 in the second.
Over the first five innings, the Orioles wasted repeated opportunities to score.
Mariners GM Jack Zduriencik says manager Eric Wedge, who had a mild stroke on July 22, won't rejoin the team this week. Zduriencik said Wedge is "doing well," but added, "This is a lifelong health issue for him. When he gets back here managing this club, we want him to be here. We don't want him to come in and be here for two or three days."... Zduriencik also said RH reliever Stephen Pryor has been shut down for the year with an injured right triceps muscle. ... Orioles 2B Brian Roberts missed a third straight game while on paternity leave. He is expected to travel with the team Monday to San Diego for a two-game series that begins Tuesday night. ... The Mariners host Toronto on Monday night after going 2-4 on a six-game trip through Boston and Baltimore. ... Seattle won the season series 4-2.
Copyright by STATS LLC and The Associated Press
BALTIMORE, MD - AUGUST 04: Joe Saunders #23 of the Seattle Mariners pitches in the first inning against the...