OAKLAND, Calif. -- The Houston Astros continued their road struggles Tuesday night, and their shrinking lead in the American League West is down to one game over the Texas Rangers.

Left-hander Scott Kazmir was outdueled by former teammate Sonny Gray, and the Astros fell 4-0 to the last-place Oakland A's at the O.co Coliseum.

Kazmir faced the A's for the first time since they traded him on July 23 to Houston for a pair of prospects. He squared off against Gray, his close friend and a young pitcher he mentored in 2014 and much of this season in Oakland.

Kazmir (7-10) gave up four runs on seven hits, including a three-run homer to rookie first baseman Mark Canha and a solo shot to rookie center fielder Billy Burns, over six innings. He struck out three and walked two. Kazmir fell to 2-5 in nine starts with the Astros.

"It's always frustrating losing games, especially at a time like this when we really need to take care of business," Kazmir said. "You have to stay positive. Trust what's gotten us here this entire year, and we'll be just fine. We can't let a game like this really bother us, and we can't let it carry on for tomorrow's game and the series ahead of that."

Gray (13-7) gave up five hits in seven scoreless innings while snapping his season-high, three-game losing streak. He struck out four, walked two and threw 101 pitches.

"I had a rough outing my last time, so it was important to get back on the mound and put zeros up, give us a chance to win," Gray said. "I used my curveball a lot more to keep them off-balance."

The Astros (75-64) fell to 27-40 on the road and lost at the Coliseum for the fifth consecutive time. They are 0-2 on their 10-game road trip.

Houston's lead shrunk from 5 1/2 games to one in 13 days.

"It's crunch time here in September," Astros catcher Hank Conger said. "Everyone keeps talking, 'We're a playoff team.' We got to start showing it. We got to start bearing down and be able to at least put together better at-bats than what I did today."

The Astros had the bases loaded with one out in the second inning, but Gray struck out Conger and retired left fielder Jake Marisnick on a pop fly in foul territory.

"That was the key to the game," A's manager Bob Melvin said. "A couple of walks. His command was a little off. That was their best chance to do some damage."

A's rookie right-hander Ryan Dull pitched two perfect innings to close out the win, keeping his ERA at 0.00 over six innings since he was recalled from Triple-A Nashville.

Burns went 2-for-4 and scored twice. Canha had a pair of hits, and designated hitter Billy Butler went 3-for-4.

The A's took a 1-0 lead on Burns' leadoff home run in the third inning. It was his fourth home run of the season, all of them solo.

"It was weird," Burns said of facing Kazmir. "He was such an influential guy in this clubhouse, and I was pretty close to him. His leadership in the clubhouse was pretty awesome. It was just weird looking at him on the other team on the mound. At the same time, it was fun."

Canha extended Oakland's lead to 4-0 with his three-run shot in the fifth. Shortstop Marcus Semien walked with one out, stole second base and moved to third on Burns' single to right.

Canha crushed Kazmir's 1-0 cutter high and deep down the left field line, nearly reaching the seats in the second deck for his 14th home run of the season and sixth in his past 20 games.

"The (pitch) to Canha was something I look back on and kind of just shake my head because I feel like I had been beating him with a fastball all game and then I speed his bat up with a cutter inside," Kazmir said. "It's frustrating. That's a huge hit right there. We're trying to battle our way back, and I end up giving up a three-spot in the fifth inning. That's tough to come back from, especially with a guy like Sonny on the mound."

NOTES: Oakland recalled OF Craig Gentry and rookie INF Max Muncy from Triple-A Nashville. ... A's C Stephen Vogt, who missed his second consecutive game since being hit in the groin by a foul ball Sunday, will not have to undergo surgery. "So now it's going to be all about when he's able to move around and play," A's manager Bob Melvin said. ... Astros LHP Tony Sipp, who has not pitched since Aug. 26 due to a sore back, played catch pain-free two straight days and will throw a bullpen session Wednesday or Thursday in Houston, manager A.J. Hinch said. ... Astros C Jason Castro, on the disabled list since Aug. 29 because of a strained right quad, is running on a treadmill and hitting. He might catch Sipp's bullpen session this week.