For a second, Astros reliever Enoli Paredes looked like he might panic as he slipped fielding Marcus Semien’s comebacker with two outs in the seventh inning. He was protecting a three-run lead, but the middle of Oakland’s lineup loomed if Semien reached base.

Paredes, however, was confident.

“I was 100% [certain] that I can make that out,” Paredes said later. “I lost the ball for a little bit, but when I make sure to get the ball, I just [had to] be ready to throw a good throw to first base to get a big out. I don't feel nervous or anything, because I have everything in control. So just find the ball and make the throw.”

Paredes gathered himself, fielded the ball and threw from his knees to first base, then pounded the infield in celebration with the inning over. It might have been emblematic for the way a lot of Astros fans were feeling as Houston erased an early deficit and pulled away for a 10-5 win over the A's to open the American League Division Series on Monday at Dodger Stadium.

For an Astros team that has played in five of the last six postseasons, advancing to two World Series, there’s a key difference this year -- their bullpen is almost entirely new. The young relievers that manager Dusty Baker leaned on in Game 1 all donned orange, but other than closer Ryan Pressly, they were fairly green.

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Compared to Oakland bullpen's MLB-best 2.72 ERA in the regular season, Houston’s 'pen inexperience looked like a potential difference in the series. On Monday, the Astros' relievers were the difference in the win. After the A’s hit three homers in four-plus innings off Lance McCullers Jr., Houston's bullpen delivered five hitless innings with one walk and five strikeouts. Four of those innings came from rookies. Three came from relievers for whom Monday marked their first postseason appearance.

“They've been forced to grow up and learn some valuable lessons the hard way sometimes,” Baker said. “That's on-the-job training, you know, but those guys, they came in and they did a great job against an offense that was rolling pretty good.”

The Astros' bullpen, which posted a 4.39 ERA in the regular season, has tossed 14 2/3 scoreless innings this postseason. Five innings came in a piggyback outing at Minnesota for Framber Valdez, who will start against the A’s in Game 2 on Tuesday. Hard-throwing Josh James, who pitched in nine postseason games last year, remains fresh, as does lefty Brooks Raley. Pressly, however, appears set to be tested.

McCullers kept the game close by stranding runners at second and third in the fourth inning. But after an infield single and an error put Semien on second for the middle of the lineup in the fifth, Baker turned to lefty Blake Taylor, who had pitched in just three games above Double-A before delivering a 2.18 ERA and allowing a .173 batting average in 22 games for Houston this year.

Pinch-hitter Chad Pinder’s groundout advanced Semien for Mark Canha’s sacrifice fly and a 5-3 A’s lead, but that was it. Once a four-run sixth moved Houston in front, in came Paredes, who powered his way from Double-A last year to a vital role in the Astros' bullpen this season to protect a two-run lead.

Fittingly, Paredes came out firing fastballs -- 95, 96 and 97 mph -- to strike out Khris Davis to begin the inning. Paredes threw just 11 pitches in the sixth inning, 10 of them fastballs. The exception was the slider that struck out Robbie Grossman.

“[Catcher] Martin [Maldonado] was calling the pitches. I just meant to make quality pitches,” Paredes said. “I was ready with all my pitches.”

With Oakland’s 9-1-2 hitters due up in the bottom of the seventh and Houston’s lead up to 8-5, Baker stuck with Paredes. Eight of his 10 pitches in the seventh inning were fastballs, including all five to Tommy La Stella. Paredes started off Semien with a slider, then made his infielder-like recovery to fire a fastball to first base to end his outing.

With the middle of Oakland’s order due up in the eighth, on came Cristian Javier, a candidate to start a game later this series. He overcame a leadoff walk for a clean inning, capped by strikeouts of Matt Olson and Davis. Though two runs in the ninth stretched the lead to five, Pressly retired the bottom of the lineup in order.

That inning could be the lone constant as Baker mixes and matches to get the lead to Pressly, who posted a 2.84 ERA in seven appearances when working on back-to-back days. He hasn’t pitched on three consecutive days since June 28-30 last year -- something the Astros could call on him to do in this series -- but he pitched both ends of a Aug. 29 doubleheader this season, tossing two perfect innings with four strikeouts for two saves -- against the A’s.