OAKLAND -- Jim Riggleman never saw enough of Cesar Jimenez during Spring Training to form an opinion on the young left-hander.

"There were so many guys there, especially left-handers, and I would not have distinguished who he was," the Mariners interim manager said Monday. "I know he didn't pitch many innings."

Jimenez appeared in five Cactus League games, worked 4 1/3 innings, walked two, struck out two and allowed three earned runs. Nothing he did really stood out, and, as expected, he started the regular season in the Minor Leagues with Triple-A Tacoma.

But Jimenez left a favorable impression on Mariners pitching coach Mel Stottlemyre.

"I really liked him in Spring Training," Stottlemyre said, "and if we had had more room, I would have liked to have put him on the roster."

Stottlemyre became a little more of a Jimenez fan on Sunday afternoon at Safeco Field.

Pressed into duty during Seattle's 15-inning marathon game against the Tigers, Jimenez tossed four hitless innings, allowing only two baserunners.

The Mariners eventually lost the game -- with catcher Jamie Burke surrendering the decisive run -- which took away some of the attention Jimenez deserved.

"What he did, in rising to the occasion the way he did, was more than we could have asked for," Stottlemyre said. "If we had won the game, he would have been a big part of it. He set himself up for times to get the win, but we couldn't get a run off their bullpen."

Jimenez sat in front of his locker in the visiting clubhouse at McAfee Coliseum on Monday afternoon, using a piece of metal to exercise his left arm. The four innings he worked on Sunday were the most he had worked during any game this season.

The 57 pitches he threw also were a season high.

"He convinced me that there is no doubt he belongs in the big leagues, as long as he pitches like that," Stottlemyre said. "He mixes his pitches well and spotted his fastball very well. Yesterday, he went way beyond what we thought he could do."

That is music to Jimenez's ears.

"I want to show them that I can pitch up here," the 23-year-old said. "I know they have to make a decision later this week when they activate Felix [Hernandez] and even if I have to go back [to Tacoma], I hope I showed them what I can do."

The Venezuela native had a 1-3 record and 3.55 ERA in 29 relief appearances for Tacoma. When Hernandez went on the disabled list on June 24, Rainiers manager Daren Brown recommended Jimenez as a replacement.

It was a good choice, as Jimenez has yet to surrender a run in 6 2/3 innings, allowing only one hit.

"The only concern was he had not been stretched out more than two innings and had not pitched two days in a row," Riggleman said. "We've already had him pitch two days in a row and four innings."

Jimenez was unavailable for the Mariners series opener against the Athletics on Monday night, but he could be good to go on Tuesday night.

"His breaking ball is a work in progress, but he's not a guy you can only use against left-handers," Riggleman said.

"I have been working on my slider and I feel confident enough to throw it in any situation, in any count," Jimenez said.

"When we sent him down, we wanted him to work on breaking stuff to left-handers," he said. "It definitely has improved. He already spots his fastball and has a great changeup."

He also has a much stronger resume, thanks to his Sunday afternoon outing at Safeco Field.