A strike call Jarrod Parker thought he deserved but didn't get cleared the way for a big inning that cost the Oakland Athletics dearly in an 8-3 loss to the Arizona Diamondbacks on Saturday night.

The A's right-hander — and former Diamondback top prospect — thought he should have gotten a called third strike against Justin Upton in the fifth inning. Instead, it was a ball and Upton followed with an RBI double. Two batters later, Miguel Montero hit a grand slam and the Diamondbacks were off to their fourth straight win.

"I thought I made a strikeout pitch and didn't get the call I wanted," Parker said. "I went back there and he made an adjustment and hit it. It is one of those pitches that can go either way and it went against us."

Parker called it "definitely frustrating."

"That is a pitch that if it goes my way then we are out of that inning and we move on," he said. "Obviously that was a big inning after that. The wheels kind of fell off and it hurt us."

Manager Bob Melvin apparently agreed with Parker's assessment of the pitch. He was ejected by home plate umpire Tim McClelland after the inning 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."

After taking three of four from Texas, the A's have lost two straight in the desert, the 9-8 heartbreaker Friday night, when Ryan Roberts won it for Arizona with a two-out, three-run homer in the ninth, followed by Saturday night's one-sided defeat.

Oakland tries to avoid a three-game sweep when the teams meet in the finale of the interleague series on Sunday.

Trevor Cahill outpitched Parker (2-3) in a matchup of starters traded for each other last offseason.

Jason Kubel had two RBI singles and Paul Goldschmidt extended his hitting streak to 16 games for the Diamondbacks, who have scored 33 runs in their four-game streak.

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.

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.

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.

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.

NOTES: 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 the homer to Roberts to blow a save in Friday night's 9-8 loss. ... Melvin says OF Yoenis Cespedes, out for two games with a strained left hamstring, could be available to pinch-hit on Sunday.