The Mariners lead the Major Leagues with a 2.95 ERA, but manager Lloyd McClendon has concerns about his starting rotation.
In the midst of a huge playoff push -- Seattle has won 15 of its last 21 games -- several starters have shown signs of slowing down, albeit slightly.
James Paxton, who will take the hill on Tuesday night in the middle of three home games against the Rangers, has been injured for most of the year, so he is probably not fatigued. But he was one of four Mariners' hurlers to have a subpar outing on the team's recent 6-3 road trip.
Paxton took his first career loss Wednesday in Philadelphia, allowing just one earned run but four total as he lasted four innings, struggling with his control.
"I've been concerned about that all year. That's why we've done everything we can to push them back whenever we get the chance to do that," McClendon said Monday of the possibility of overworking the starting pitchers.
"I think you probably saw a little bit of the grind," he said. "They'll probably tell you different -- that they weren't tired -- but if you really think about it ... our starting pitching was not very stellar."
Nick Martinez will start for the Rangers on Tuesday, carrying a 2-1 record with a 4.24 ERA in his last three starts. He allowed two runs in six innings in a 5-4 win over the Marlins on Wednesday.
"The last three starts have been different," Martinez said. "I think I'm a different pitcher. I've learned a lot about recognizing situations and at-bats, and I've learned a lot about myself and handling situations, pressure situations."
Martinez, 24, has thrown 100 innings at the big league level and another 9 2/3 innings at Double-A Frisco. He threw 151 1/3 innings in the Minor Leagues last season so he is on target to come close or exceed that with potentially seven starts remaining this season.
"I definitely still feel strong," Martinez said.
Rangers: Choice back in big leagues to play
Michael Choice returned to the big leagues on Monday and will join the outfield rotation that already includes Daniel Robertson and Jim Adduci. Choice is expected to start against Paxton on Tuesday but won't be used exclusively as a platoon option against left-handers.
"Michael Choice is not here to sit," manager Ron Washington said. "If he gets hot, I'm going to ride that horse."
Choice began the season with the Rangers but hit .177 with eight home runs and 28 RBIs in 69 games. The Rangers sent him down to Triple-A Round Rock on July 7 and he hit .267 with seven home runs and 31 RBIs in 43 games there.
The Rangers were expected to call him up in September when rosters expand, but he arrived a week early when Shin-Soo Choo went on the disabled list with a bone spur in his left elbow.
Mariners: Felix pushed back to Friday
McClendon took one step on Monday toward giving his starters some extra rest, announcing that ace right-hander Felix Hernandez will pitch Friday on six days' rest instead of making his start originally scheduled for Wednesday.
Seattle has yet to announce who will pitch Wednesday against the Rangers, but there are two logical candidates with recent big league experience: righties Erasmo Ramirez and Taijuan Walker.
McClendon confirmed that Ramirez or Walker will join the club in some capacity Sept. 1, when rosters expand from 25 to 40. If one of the pitchers is recalled before then, it would require a corresponding roster move.
Hernandez will face the Nationals on Friday in the opener of a three-game set at Safeco Field.
• No active Rangers player has faced Paxton in a Major League game. Prince Fielder, who is on the disabled list and out for the season, had three at-bats against him last season while with the Tigers.
• The Rangers are in the process of finalizing their September callups. Among the candidates to be called up are pitcher Spencer Patton and infielders Luis Sardinas and Ryan Rua.
• The Mariners entered Monday averaging five runs per game since the July 31 non-waiver Trade Deadline. Prior to that, they averaged 3.83 runs per game.
Aaron Leibowitz is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.