PHOENIX -- Miguel Montero says he was anxious to join the party the Arizona offense has been throwing lately.
A grand slam should make him a member in good standing.
Montero hit his second career slam and the Diamondbacks beat the Oakland Athletics 8-3 on Saturday night for their fourth consecutive victory.
"I just felt like I wanted to get into the groove," Montero said, "because all of the guys are swinging the bat really good."
Trevor Cahill outpitched the Athletics' Jarrod Parker (2-3) in a matchup of starters traded for each other last offseason.
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Jason Kubel had two RBI singles, Justin Upton doubled in a run and Paul Goldschmidt extended his hitting streak to 16 games for the Diamondbacks, who have scored 33 runs in their four-game streak.
"They say hitting's contagious," said Kubel, who raised his average to .300, "and it's going so well right now."
Cahill (4-5), coming off a shutout against San Diego, gave up two runs and seven hits in 7 1/3 innings. He had a season-high seven strikeouts and walked three.
"I was probably more nervous than any other start this year," Cahill said, "just going against the team I played for. I was there for six years in the minor leagues and big leagues, so it was definitely a little bit more nerve-wracking."
Cahill was 0-3 in four home starts before getting the win Saturday night.
The Diamondbacks matched their longest winning streak of the season, set when they started the year 4-0. Arizona has won six of seven overall and, for the first time this season, taken three consecutive series.
Parker, who threw eight innings of one-hit ball against Texas in his previous start, gave up six runs and eight hits in five innings. He struck out four and walked five, two intentionally.
Plate umpire Tim McClelland ejected Oakland manager Bob Melvin between the fifth and sixth innings for arguing balls and strikes.
"I was just arguing," Melvin said. "It doesn't make any difference now. Over the course of the game there are going to be some pitches that either miss or are close, or whatever. It goes both ways. You see it one-sided a lot of times."
Cahill and Parker were locked in a 1-1 duel when Arizona broke it open with a five-run fifth.
With one out, Gerardo Parra and Willie Bloomquist singled to put runners at first and third, then Upton laced a 3-2 pitch into center for an RBI double.
Parker thought he had struck out Upton "but didn't get the call I wanted."
"It is definitely frustrating," Parker said. "That is a pitch that if it goes my way, then we are out of that inning and we move on. Obviously that was a big inning after that. The wheels kind of fell off and it hurt us."
The A's intentionally walked Kubel to load the bases for Goldschmidt, who struck out on a 3-2 pitch. That brought up Montero, who drove a 1-1 pitch over the swimming pool in right field for his first slam since Aug. 16, 2008, at Houston.
Parker's string of 18 scoreless innings ended in the first. Bloomquist singled and stole second, then came home on Kubel's two-out single.
Oakland tied it in the second. Brandon Moss drew a two-out walk, then scored from first when Kurt Suzuki doubled down the right-field line.
Cahill left after walking two batters in the eighth. Brad Zeigler came on and gave up a single to Brandon Inge to load the bases. Pinch-hitter Jonny Gomes then delivered a sacrifice fly.
Arizona padded the lead with RBI singles from Kubel and Goldschmidt in the eighth.
Parker was one of a handful of top Arizona pitching prospects when the Diamondbacks sent him, right-handed reliever Aaron Cook and outfielder Colin Cowgill to Oakland for Cahill, left-handed reliever Craig Breslow and cash.
Goldschmidt struck out three times before his eighth-inning hit. ... The Diamondbacks have agreed to terms with 31 draft picks, including first-round selection Stryker Trahan. The catcher from Acadiana High School in Lafayette, La., the 26th selection overall, took batting practice with the team. ... Two left-handers go in the series finale on Sunday, Travis Blackley (0-1, 3.45 ERA) for Oakland and Joe Saunders (3-4, 3.65 ERA) for Arizona. ... With a win on Sunday, the Diamondbacks (29-30) would reach .500 for the first time since they were 7-7 on April 20. ... Melvin was ejected for the third time this season. ... Before the game, Melvin said he would go to closer by committee after Brian Fuentes gave up a three-run homer to Ryan Roberts to blow a save in Friday night's 9-8 loss.