In his first start, Kris Benson had stamina problems. In his second start, he had focus problems. So last night’s third start was an important one for the Mets right-hander, slotted as the no. 3 man in their rotation.

Benson delivered, limiting Cincinnati to four hits in 7 2 /3 innings in the Mets’ 9-2 win over the Reds. He struck out eight, walked two, and left feeling good about what he had done.

“I stuck with my game plan, with what I’ve been concentrating on,” Benson said. “I feel like I’m getting back in the groove., Hopefully, I can continue with good outings.”

Mets manager Willie Randolph hopes so, too.

“Benson is a key for us,” he said. “He’s our no.3. He came in and dominated. He had a good slider, a sinker down in the zone, and good movement.”

Benson (1-1), who began the season on the disabled list with a strained chest muscle, allowed just two hits after the second inning and retired 10 straight batters from the second through the sixth. Dae-Sung Koo relieved with two outs in the eighth.

“The longer I pitch, the better I feel,” he said. “I feel now I’m where I need to be. I feel more relaxed. Today was a big jump. I threw a lot of pitches and I had a good outing.”

Benson benefited from six extra-base hits, one of them the 11th homer of the season by Cliff Floyd. The Mets scored four runs in the first two innings and provided a comfort zone for Benson.

Benson was backed with 13 hits. Jose Reyes led off the first with a triple to right center, his first three-base hit of the season. After Mike Cameron struck out looking, Carlos Beltran scored Reyes with a sacrifice fly.

Floyd then lined a 2-2 pitch from Paul Wilson (1-5) into one of the mezzanine suites in right field. On Friday night, he banged a pair of 400-plus foot shots off the right field scoreboard. He is now tied for the NL lead in homers.

The Reds picked up a run in the second when Adam Dunn singled, moved to third on a wild pitch that Mike Piazza couldn’t locate, and scored on a two out single by Jason LaRue.

But the Mets made it 4-1 with two more in the bottom half of the inning. Doug Mientkiewicz opened with a single and raced to third on a double by David Wright. Kaz Matsui’s sacrifice fly scored Mientkiewicz, and Wright came home when Benson singled to left and Dunn kicked the ball for an error.

The Reds scored again in the sixth when Ryan Freel opened with a walk and came home on a double by Felipe Lopez. After Lopez advanced to third on an infield out, Ken Griffey Jr. flied to right and Cameron cut down Lopez trying to score after the catch with a perfect throw to Piazza.

Floyd opened the Mets sixth with a walk, moved to third on a double by Piazza, and scored on a sacrifice fly by Mientkiewicz. Wright’s second double scored Piazza and finished Wilson. Matsui then singled home Wright.

In the seventh, Beltran singled, raced to third on a single by Piazza, and scored on an infield out. Piazza then took third on a wild pitch and scored when LaRue threw the ball into left field.

Before the game, the Mets optioned outfielder Victor Diaz to Triple-A Norfolk to make room on the roster for pitcher Kaz Ishii, who will be activated from the disabled list and start tonight.

Diaz started the season in right field while Mike Cameron was on the disabled list and set Mets rookie records with 10 RBI and 16 runs during April. He was batting .294 with four home runs and 15 RBI.

The Mets also placed catcher Ramon Castro on the 15-day DL due to a strained right quadriceps and purchased the contract of catcher Mike DiFelice from Norfolk.