SEATTLE -- Thirty-five-year-old starter Hisashi Iwakuma looked as if he had thrown his last pitch for the Seattle Mariners when he signed a free agent deal with the Los Angeles Dodgers in early December.

When he failed a physical with the Dodgers, there seemed to be a possibility that he had thrown his final pitch for anyone.

Eight months later, having re-signed with the Mariners on Dec. 17, Iwakuma is leading Seattle back into postseason contention.

Iwakuma held an opponent scoreless for the second start in a row Monday, outdueling Detroit rookie Michael Fulmer to lead the Mariners to a 3-0 win over the Tigers.

Seattle (58-53) has won six of seven games to move within 2 1/2 games of Detroit in the race for the American League's final wild-card spot.

"We're on a streak right now, and we don't want to stop the streak," Iwakuma said through an interpreter. "It's the first game of the series, and you always want to win the first game, so I'm just glad I could contribute to that."

Iwakuma (13-7) threw seven scoreless innings, allowing just five hits, before new Mariners reliever Arquimedes Caminero and rookie closer Edwin Diaz finished off the win.

Diaz, who replaced Steve Cishek as closer last week, now has five saves in as many chances.

Fulmer (9-3) took his first loss since June 17 despite giving up just two runs on five hits over seven innings. He had won seven of eight decisions dating back to May 10.

"Michael Fulmer wasn't as sharp as he has been in the past," manager Brad Ausmus said.

Detroit (61-51) dropped its second game in a row to fall 2 1/2 games behind the Cleveland Indians in the American League Central standings.

Kyle Seager, Mike Zunino and Guillermo Heredia each had an RBI single for the Mariners, who took a 2-0 lead in the second inning and added a run on Heredia's single in the eighth.

The only Detroit baserunner to get past first base was Ian Kinsler, who led off the game with a walk and moved to second on a one-out single from Miguel Cabrera but ended up stranded there.

The Tigers, who had not been shut out since July 8, have scored just one run over their past two games.

"We just couldn't get much going offensively," Ausmus said.

Nelson Cruz went 2-for-3 with a double and a run for the Mariners, who had just seven hits.

"You're not going to get home runs every day (or) hits every day," Cruz said. "You're going to need pitching, and today was a good example."

Diaz, a 22-year-old rookie who began this season as a Double-A starter, retired all three batters in the ninth inning. He has a 1.80 ERA over 29 appearances since getting called up on June 4.

With a fastball that reached 98 mph Monday, Diaz got three Detroit batters on eight pitches. However, Ausmus didn't seem overly impressed with the rookie's high-90s fastball.

"He throws hard," Ausmus said when asked about Diaz's success. "He certainly has some impressive numbers. The truth is, you see guys throwing 98 miles per hour all the time now. They had a guy (Caminero) throwing 98 in the eighth. It's not as rare as it used to be."

Caminero was making his Mariners debut after getting traded from the Pittsburgh Pirates over the weekend.

The Mariners jumped out to a 2-0 lead on RBI singles from Seager and Zunino in the second inning.

Seager followed Cruz's leadoff double with a single up the middle, giving Seattle a 1-0 lead. After a one-out walk, Seager scored on Zunino's single to left.

NOTES: Detroit CF Cameron Maybin (thumb) took batting practice before the game but still wasn't in the lineup. Maybin missed the Tigers' previous four games and is scheduled to undergo a second MRI on Tuesday. Tyler Collins got the start in center field Monday. ... Seattle RHP Arquimedes Caminero, acquired from the Pirates on Saturday, was added to the active roster Monday. The Mariners optioned RHP Taijuan Walker to Triple-A Tacoma. ... INF Mike Freeman got his second consecutive start after going 2-for-3 in his Mariners debut Sunday. Freeman gave 2B Robinson Cano his first day off of the season Sunday, and he was back in the lineup Monday because SS Shawn O'Malley had a cold. With SS Ketel Marte possibly coming off the disabled list Tuesday, Freeman might be headed back to Triple-A. ... Detroit's scheduled Tuesday starter, LHP Daniel Norris, would be making his first start since July 4. He was promoted from Triple-A Toledo on Sunday.