SAN FRANCISCO(AP) Brad Penny believes San Francisco can contend for the World Series next year, which is why the right-hander isn't ruling out a return to the Giants.

Penny, who is eligible for free agency in the offseason, pitched his first complete game in more than four years to help San Francisco beat the Arizona Diamondbacks 4-1 on Wednesday night, less than two hours after the Giants were eliminated from playoff contention.

Penny allowed six hits, walked one and struck out five to remain unbeaten in four starts this season at AT&T Park since being claimed off waivers from Boston.

''I like it here,'' Penny said. ''If they make a couple moves, this team could be playing in the World Series next year. It's definitely a place I'm going to consider.''

San Francisco, clinging to slim postseason hopes at the start of the game, was knocked out of the playoff race when NL wild card-leading Colorado beat Milwaukee 10-6 earlier in the night.

The Giants have several personnel decisions to make in the offseason. The club is long on pitching but short on offense, one of the primary reasons San Francisco struggled in September during the heart of the playoff chase.

Penny would likely remain as the team's fourth or fifth starter if he's re-signed, but the two sides have yet to discuss that possibility.

''That's something we'll see at the end of the season,'' Giants manager Bruce Bochy said. ''But what a great acquisition. When you get a guy like this, he's a real shot in the arm and that's what we were looking for being in this thing. He did all that we could ask for and more.''

Stephen Drew had two hits for Arizona, which scored its only run on a throwing error by Penny in the fourth.

The Diamondbacks finished 8-18 in September, their worst month of the season.

''We scratched out a few singles but we couldn't put anything together,'' Arizona manager A.J. Hinch said. ''It was (Penny's) night. He pitched a great game and we didn't offer a ton of resistance.''

Penny (4-1) kept the Diamondbacks off balance after struggling with his command early. He pitched with runners on base in the first four innings but worked out of trouble each time. He retired 16 of the final 17 batters in his fourth career complete game and first since Aug. 14, 2005, against the New York Mets .

But as San Francisco's hired gun, Penny's success was overshadowed by the Giants being eliminated from the wild-card race.

''The whole goal here was to get into the playoffs and it's disappointing,'' Penny said. ''It does take away from how you pitched in September, but it's nice to finish strong.''

The Giants were scoreboard watching the entire night, knowing any loss on their part or a win by the Rockies would end their playoff hopes. When Colorado topped Milwaukee while San Francisco was in the field during the seventh inning, reality set in.

''We saw the score,'' Bochy said. ''We knew the last few days that it was a longshot. We just didn't play our best baseball this month.''

Eli Whiteside had a career-high three hits while subbing for starting catcher Bengie Molina . Molina, whose two home runs helped San Francisco beat Arizona 8-4 on Tuesday night, is scheduled to start the series finale Thursday in what may be his final home game in a Giants uniform.

If Molina doesn't return, Whiteside and Buster Posey - the team's 2008 first-round draft pick who hit .325 with 18 homers and 80 RBIs in the minors this year - will take over behind the plate.

Whiteside helped the Giants get off to fast start against Kevin Mulvey , hitting a two-run single in San Francisco's three-run second.

The Diamondbacks pushed across an unearned run in the fourth when Gerardo Parra reached on a fielder's choice and scored on Penny's errant throw on Eric Byrnes ' slow roller. The big right-hander hit Byrnes in the back, with the ball rolling near Arizona's bullpen as Parra raced around the bases.

Whiteside hit a drive to left in the bottom half for his second career homer, the first coming Aug. 5 against Houston.

Mulvey (0-3) retired the final seven batters he faced and yielded five hits in six innings.

NOTES: Giants 2B Freddy Sanchez had surgery to repair a torn meniscus in his left knee. Manager Bruce Bochy said Sanchez should be ready for spring training. ... Mulvey, claimed off waivers from Minnesota on Sept. 1, singled in the third for his first major league hit. ... The Diamondbacks will start RHP Daniel Cabrera against the Chicago Cubs on Saturday. Cabrera has pitched in relief since being called up from the minors on Sept. 6.