PHOENIX -- Carlos Lee was out of the starting lineup on Monday for the first time since July 10, giving J.D. Martinez a chance to hit cleanup for the first time as a Major Leaguer. Martinez showed his worth in that spot by cranking an opposite-field, three-run homer in the first inning.

"That's cool," Martinez said of batting fourth. "I've always hit three, four or five over my career, and I'm pretty comfortable here."

Lee, who was 3-for-20 on the Astros' recent homestand, has been playing first base since Brett Wallace was sent to the Minor Leagues. With Lee out of the lineup, Matt Downs made his second start of the season at first base.

"I just thought that this was a good day to give him a day and get Downs in there," Astros manager Brad Mills said of the decision to sit Lee. "[Downs] needs to play. I'm leaning towards giving [Angel] Sanchez a start [Tuesday] and trying to get those [bench] guys some starts as we move on."

Third-round pick Armstrong feeling strong

PHOENIX -- A week away from the deadline for teams to sign players selected in June's First-Year Player Draft, Astros third-round pick Jack Armstrong -- a 6-foot-7 pitcher from Vanderbilt -- isn't concerning himself with the approaching deadline.

"I'm not too anxious," he said. "My dad [former Major League pitcher Jack Armstrong] has done a good job making sure I'm focused on what matters, and that's playing baseball and pitching. Whatever happens, happens. I have two good options next year, either going back to school or signing with the Astros."

Armstrong, who has one year of eligibility remaining at Vanderbilt, has been pitching in the Cape Cod League this summer to re-establish his value. He experienced some tightness in his elbow late last month and has been moved to the bullpen, but Armstrong said Monday that he's healthy and hoping to make a start in the Cape Code League playoffs.

"I'm feeling really good," he said. "I threw an inning a couple of days ago and it felt good. [The injury] was just a little too much, too soon after my college season, and being a relief guy and then jumping into 70, 80 pitches right away. It's nothing major."

Astros assistant general manager/director of scouting Bobby Heck expects Armstrong to come to Houston for a physical as soon as his Yarmouth-Dennis team is eliminated, which could happen later this week. First-round pick George Springer, who's also unsigned, passed a physical last week in Houston.

"We've gotten signs that [Armstrong] wants to start his professional career, and we plan to be aggressive with him," Heck said. "Obviously it's a lifetime between now and Monday night. It's something we think is going to go down to the end, not because we're far apart in negotiations, but just because we're working with him still playing. The plan is to get him here in front of [team medical director] Dr. [David] Lintner at some point. The physical part is going to be imperative to the negotiating process."

Altuve reflects on returning to Chase Field

PHOENIX -- When second baseman Jose Altuve went 2-for-3 with a double for the World Team in the All-Star Futures Games last month at Chase Field, he couldn't have dreamed that he would be returning to the same venue a month later as a Major Leaguer.

Altuve, called up from Double-A Corpus Christi on July 19, took some time Monday to reflect on his return to Chase Field before hitting a double and scoring in his first at-bat against the D-backs.

"When I first came over here and saw this field, I was like, 'Wow, I would like to play on fields like this every day,'" Altuve said. "I didn't think about playing here this year. To come here again and play with the Astros, it's hard to believe it really happened."

Altuve has hit safely in 14 of his first 18 Major League games, beginning his career with a seven-game hitting streak. He hopes to continue to have success at Chase Field.

"I feel pretty good, pretty comfortable on this field," he said. "I hope to do it again."

Schafer hits balls off tee, is progressing

PHOENIX -- Center fielder Jordan Schafer, who's been on the disabled list with a broken finger since he was traded to the Astros from the Braves on July 31, hit balls off a tee for the second day in a row on Monday and is pleased with his progress.

"It feels a lot better," said Schafer, who hasn't played since breaking the middle finger on his left hand while with the Braves on July 26. "It's just a matter of how I feel every day and how it progresses."

Astros manager Brad Mills said that Schafer will likely be sent out on a Minor League rehab assignment around Aug. 20. He will then play three or four games before being activated sometime prior to the Sept. 1 date when rosters can be expanded.

Schafer is hoping to take batting practice in the next couple of days.

"Just as long as it keeps progressing, I'll be alright," he said.

Worth noting

Astros manager Brad Mills said that he'll wait to announce a starting pitcher for Wednesday's game until after Tuesday night's game against the D-backs. Mills wants to gauge the workload of reliever Aneury Rodriguez, who could make the start if he doesn't pitch too many innings in relief.