CHICAGO -- The American League Division Series opened with a Game 1 win with Astros ace Lance McCullers Jr. on the mound in Houston. McCullers was on the mound again to start Game 4 in Chicago, and the right-hander tossed four innings of one-run ball in the Astros’ 10-1 ALDS-clinching win over the White Sox at Guaranteed Rate Field on Tuesday afternoon.

But the outing may have been a costly one for Houston. Astros manager Dusty Baker said he had to pull McCullers after four innings because he was feeling discomfort in his forearm. McCullers is being further evaluated for the American League Championship Series.

“I just started getting tight at the beginning of the [fourth] inning,” McCullers said. “I got out of it. I was fine, but in a 5-1 ballgame, especially with how they came back on us a few nights ago … I felt like we had the day off yesterday, so our guys were pretty rested up.

“I just told them, 'Listen, I'm not 100 percent.' I pitched the whole fourth inning like that. I could probably do it, but I [didn't] think it would be the best idea, and so they went to the 'pen and did a masterful job.”

The decision to remove McCullers was an easy one for Baker.

“At that point in time, you know, we’ve certainly got to take care of him,” Baker said. “We can't take any chances of injury, and I only pulled him because he was hurt. That was disheartening news to me when the trainer came over and said that we had to take him out of the game. Lance is a warrior, and for him to come out of a game of that magnitude ... it had to be something, and we tried to stop it before it got serious.”

José Urquidy was originally scheduled to start Game 4, but with the contest getting postponed a day due to inclement weather in the Chicago area, McCullers got the nod on regular rest to close the series and clinch the Astros’ fifth straight ALCS appearance.

In two starts against the White Sox in the ALDS, McCullers tossed 10 2/3 innings, allowing just one run on nine hits with nine strikeouts. While he issued no walks for the first time this year in his Game 1 start, McCullers issued three free passes in Tuesday’s win. He was pulled after four innings at 73 pitches, having allowed five hits -- one of which was a solo homer to Gavin Sheets.

McCullers said he could have continued into the game after the fourth inning. However, after talking with pitching coach Brent Strom, they both decided it would be best for McCullers to come out of the game and let a rested bullpen work with a 5-1 lead at the time.

“I won’t know until we get a final analysis. I’d hate to speculate right now,” Strom said. “I’m praying for a best-case scenario. If it’s not to be, we have other capable starters. Right now, I’m very optimistic that he’ll be fine.”

McCullers added that he didn’t think it had anything to do with his ligament, but he still doesn’t expect to pitch for at least five or six days. The ALCS begins on Friday in Houston.

Five pitchers combined to throw five scoreless innings to secure the win. Strom noted that having the game postponed due to weather helped the bullpen with an extra day of rest, knowing the pitchers could go multiple innings if necessary.

“When Lance McCullers is on the mound, he is our ace, and we feel very confident when we go in the game that we're going to win that game,” said shortstop Carlos Correa. “And he was able to shut them down once again. Then the bullpen came in for five innings, did a great job. I mean, Phil [Maton] was unbelievable going one-plus, and the rest of the guys just pounding the strike zone, giving us a chance to just keep that lead and eventually win the game.”