New York Yankees activate Giancarlo Stanton from injured list, place Nestor Cortes on IL with gro...

OAKLAND -- The New York Yankees welcomed Giancarlo Stanton back to the starting lineup but suffered yet another blow to their pitching staff, with Nestor Cortes Jr. going on the 15-day injured list with a Grade 2 left groin strain.

Cortes said that he first felt the groin discomfort during his "second or third pitch of the game" against the Toronto Blue Jays last Sunday.

"During the game I didn't think it was that big of a deal. And obviously, I wanted to compete and give my team the best chance as possible," Cortes explained of his performance in the 4-2 win over the Blue Jays. "I grinded through it. I didn't know how bad it was until the MRI. Even the next day I thought it was OK, but the fact I was limping, we needed the MRI."

Manager Aaron Boone said it was catcher Jose Trevino who motioned to him after Cortes' first couple of pitches to point out something was going on, but that the lefty was able to grind through and pitch six innings of one-run ball in the Yankees' only win of the four-game series.

"I think in the heat of the moment my body was feeling right," Cortes said. "All the muscles were already fired up, so it didn't feel that bad. I think if it would have been worse, I would have probably taken myself out of the game. But the fact that I was in the game, in the moment the adrenaline was rushing, it didn't feel that bad."

As for Stanton, he was back in the Yankees' lineup on Thursday for the first time since July 23, after being diagnosed with left Achilles tendinitis. Stanton went through his entire pregame routine and took live batting practice at the Oakland Coliseum before batting third as the designated hitter.

Boone said that Stanton felt pain-free and ready to go, and so it seemed after he ripped a two-run single in his second at-bat since returning from IL. Stanton's single was 117.7 mph off the bat and gave the Yankees an early 4-0 lead over the Athletics in the second inning.

Stanton finished 1-for-4 with 3 RBIs, a walk and a strikeout in New York's 13-4 win.He said he came through the game without pain and expects to be back in the lineup at DH on Friday.

"I felt pretty good. I was pretty happy with my bats," Stanton said. "I was in and out of my timing a little bit, pitch-by-pitch, a little expected, but I think I did a decent job of making adjustments mid at-bat."

Boone said before Thursday's win that Stanton will DH "in the early going" and will build himself up to be in the mix to play outfield in future games.

The Yankees promoted minor league right-hander Greg Weissert to replace Cortes Jr. in the active roster. Outfielder Harrison Bader (plantar fasciitis) was also transferred to the 60-day injured list.

Cortes has been one of the best pitchers in baseball this season, posting a 2.68 ERA over 131 innings and making his first All-Star Game earlier this season. He has blown past his previous career high in innings pitched and never topped more than 115 in the minor leagues. Cortes sits second in the Yankees' rotation in fWAR with 2.6, behind Gerrit Cole.

"I feel like if there was a time for it to happen it would be now instead of the middle of September or late September going into the playoffs or October," Cortes said regarding the timing of his injury. "I've got to take care of my body so I can be one of the guys when playoff time comes around."

Boone announced that righty Clarke Schmidt would take over Cortes' rotation spot and would start Sunday's game in Oakland. Schmidt has pitched 33 innings in 22 games coming out of the bullpen this season but was stretched out to pitch starter innings during his last minor league stint with Triple-A Scranton/Wilkes-Barre.

Weissert has pitched in 40 games for the RailRiders this season, posting a 1.76 ERA with 18 saves in 19 chances, and 67 strikeouts in 46 innings, all but forcing the Yankees to give him a chance to pitch in the big leagues.

"We really like him," Boone said of Weissert. "He's kind of rocketed through our system the couple of years ... he's kind of kicked his way in and we think he's a guy that can, not only just fill a spot [on the roster] but come up here and impact us."

Weissert credited learning to use "his best pitches in tight situations" as the key to his success this year. "Definitely throwing more strikes this year and getting ahead of people more consistently."

Weissert made his debut on Thursday but struggled. Inone-third of an inning, he issued a balk, hit two batters and was charged with three earned runs.

The Yankees had some good news on the injured pitching front, with Luis Severino (lat strain), who threw his first live batting practice last Tuesday, with his fastball reaching 95-97 mph, still expected to return to the rotation in September.

In terms of the relief corps, Miguel Castro (right shoulder strain) is scheduled to throw a bullpen when the club heads to Tampa the last weekend in August. Castro is also tracking to return in mid-September. Closer Clay Holmes (lower back tightness) threw a 25-pitch bullpen and is scheduled to throw live batting practice ahead of being activated during the Yankees' upcoming series in Anaheim.

ESPN's Joon Lee contributed to this report.