Right-hander Clay Buchholz, who pitches for the Red Sox, brings an 11-4 record and 4.50 ERA into the game following tough battles with the Angels in his last two starts.
Left-hander Jason Vargas (13-9, 3.90 ERA) will start for the Mariners, who have improved as the season has progressed but have spent virtually all of it in last place in the American League West.
Buchholz worked seven tough innings against the Angels on Tuesday in his last start, allowing six hits and four earned runs and leaving with a one-run lead that the Red Sox's bullpen ultimately squandered in a 6-5 loss.
Five days earlier, the Angels lit him up for 12 hits and seven earned runs over 5 1/3 innings in a game the Red Sox lost 7-3.
Buchholz has bounced back after a terrible start to the season when he had a 7.19 ERA in his first 10 starts.
Buchholz knows the reason for his problems in that first start against the Angels and the ensuing improvement in the last start.
"Missed location," he said after his last start. "If you miss your spots, they hit it hard. I've got to do a better job of commanding the fastball.
"I didn't give up seven this time. I only gave up four, so that's better than the last time out."
Failures like that bother him, Buchholz said.
"It gets under your skin when you miss location and they hit the ball really hard, and all you can think about is, 'What if I threw the ball right where I wanted to? Would it have been hit that hard?'" he said. "I've got to make adjustments and get ready for the next time I go out there."
Vargas was in the midst of a streak in which he was 6-1 with a 2.55 ERA in 11 starts before rough outings in his last two starts, when he gave up six runs each time.
Vargas is third in the American League in innings pitched at 184 2/3, not far off his career-high 201 from last season, but manager Eric Wedge said he doesn't think Vargas is hitting any sort of wall.
"This guy has worked so hard this year, just from a physical conditioning with his routine, and I think that's going to see him to the end," Wedge said. "I don't see a guy out there laboring. His arm is still working good. He's still in good shape. I think he's going to be OK."
The reason for Vargas's struggles recently?
"Just command," Wedge said. "He just hasn't had quite the same command we've seen him have really all year long."
Red Sox: Losing streak at six
After losing 6-2 to the A's on Sunday, the Red Sox have lost the first six games of their nine-game, nine-day road trip, scoring two runs or less in each game and being outscored 45-10.
The six-game losing streak is their longest of the season.
Second baseman Dustin Pedroia was 3-for-4 Sunday, extending his hitting streak to 13 games and raising his batting average to .288. It's Pedroia's third double digit hitting streak of the season. He had streaks of 14 and 13 games earlier in the season.
Mariners: Gutierrez's errorless streak continues
Center fielder Frank Gutierrez comes into Monday's game having not made an error in 296 consecutive games.
Utility infielder Ivan De Jesus, who was one of the key players picked up by the Red Sox in the recent blockbuster trade with the Dodgers, was added to the roster Sunday and will be available in case Pedroia's wife, Kelli, goes into labor in the next few days.