PHOENIX -- Tracking the ball against the tough-to-pick-up backdrop of spacious Chase Field, Brandon Allen sprinted to the corner and leaped in the air, snaring Chase Headley's slicing fly ball just before careening off the chain-link fence.

The first ball hit to him in his first big-league game as a left fielder, Allen made it look like he'd been there all along.

Oh, yeah, he hit a grand slam, too, but the Arizona Diamondbacks kind of expected that.

Making an impressive 2010 debut with Arizona, Allen hit his first career grand slam and made several rangy catches in left field to help the Diamondbacks send the Diego Padres to their seventh straight loss, 5-2 on Wednesday.

"Unbelievable," said Diamondbacks starter Barry Enright (6-2), who fought through seven not-quite-sharp innings. "I cannot say enough."

Allen's big day ruined the Padres'.

They entered the day still four games ahead of San Francisco in the National League West, but another loss at last-place Arizona wasn't what they wanted heading into a 10-game homestand against three division opponents.

Ace-in-the-making starter Mat Latos did his part to keep the Padres in it, holding Arizona to one run and four hits over six innings while matching a career high with 10 strikeouts.

The rest of it didn't go so well.

Miguel Tejada broke a 4-for-26 slump with a solo homer in the fourth inning, but had an error on a potential double-play ball to set up Allen's grand slam. Reliever Luke Gregerson (3-7) didn't help himself in the inning, either, issuing a leadoff walk and giving up Gerardo Parra's third single after Tejada's error.

The Padres went 1-for-7 with runners in scoring position, leaving Arizona with a three-game sweep by a team that's 22 games behind them in the division.

"Things aren't going our way," Padres manager Bud Black said. "We will spin out of it."

Allen made his way through Arizona's minor-league system with his bat, slugging 25 homers with 86 RBIs in 107 games at Triple-A Reno this season. He's been shaky at times with the glove at first base, though, his progress to the majors slowed even more by the signing of Adam LaRoche in the offseason.

Looking to find a way to get his bat to the majors, Arizona started occasionally sending Allen out to left field this season in Reno, an experiment that had gone relatively well because of his athleticism.

Allen earned a September call-up on Wednesday and found himself in the starting lineup, batting eighth and playing left field.

Without catching any fly balls during the warmups, the rookie brought the crowd and his teammates to their feet with his against-the-fence catch of Headley's slicer on the first ball hit to him in the fourth inning. He added an in-the-gap snag in the fifth inning and another ho-hum catch out in left later in the inning.

Then in the seventh inning, Allen did what he does best, punctuating his return to the majors with his slam off Gregerson that earned a curtain call from the fans.

"He was very comfortable out there," Diamondbacks interim manager Kirk Gibson said. "That one play, I'm not sure you understand what it's like to run into that fence like that, but he knew exactly where he was and had it perfectly timed. He's an athletic kid."

Arizona, after a tough start to the season, finally has some momentum.

Coming off their first winning month in a year (16-13 in August), the Diamondbacks followed a road series win over San Francisco with an impressive three-game sweep over the NL West leaders.

Chris Young hit his 23rd homer, Enright allowed two runs and nine hits and Juan Gutierrez pitched the ninth for his sixth save to help Arizona win for the sixth time in seven games.

"The guys have been playing good baseball, and hopefully we can keep it going," Young said. "It's nice to know we can make a difference."

Latos made it tough on them.

The right-hander struck out the side twice in the first four innings and made one just mistake: a 3-1 down-the-pipe fastball that Young turned into a curling solo homer off the foul pole in left that tied it 1-all.

That was it, though, making Latos the first pitcher to allow two earned runs or less in 14 straight starts since Greg Maddux did it with Atlanta from 1993-94.

"I did what I wanted to do," Latos said. "I tried to come out and put zeros on the board, try to keep the game close and try to win a ballgame."

With the game tight, though, Black decided to go for offense in the seventh inning, replacing Latos with a pinch-hitter.

The hitting part worked: Will Venable hit a run-scoring single to put the Padres up 2-1. The plan backfired, though, when Tejada couldn't hold onto the ball and Gregerson the lead, setting up Allen's storybook-finishing slam.

"Nobody imagines that," said Allen, who hit .202 and had 40 strikeouts in 32 games as a first baseman with Arizona last season. "Everything just falls into place."