Severino allowed four hits in six shutout innings, leading the Yankees over the Atlanta Braves 3-1 on Saturday night.
"It doesn't seem to overwhelm him, the situation here," Yankees manager Joe Girardi said.
A fan was killed at Turner Field hours earlier when he fell from the upper deck onto the lower-level stands. He was pronounced dead at a hospital.
Lt. Charles Hampton of the Atlanta Police Department's homicide unit said foul play was not suspected, pending further review by the medical examiner.
Hampton said the man was in his early 60s, and identification was being withheld pending notification of his closest relatives.
Severino (3-1) was lifted for pinch hitter Alex Rodriguez in the seventh. Soon after Rodriguez was introduced, the fan fell. There was no delay in the game while medical personnel treated the man.
Severino, making only his fifth start since his big league debut on Aug. 5, was dominant. He struck out five and walked three.
The 21-year-old Severino has allowed no more than three runs while pitching five or six innings in each start.
"That kid has got a pretty good arm," Braves manager Fredi Gonzalez said. "That's what they're supposed to look like right there."
Andrew Miller pitched a perfect ninth for his 28th save.
The Yankees remained 1 1/2 games behind first-place Toronto in the AL East with their second straight win over the Braves.
The Braves have lost four straight and 11 of 12. The sellout crowd of 49,243 was a season high at Turner Field.
Matt Wisler (5-5), also a rookie right-hander, gave up two runs on four hits and four walks in six-plus innings.
Jacoby Ellsbury led off the game with a bloop double that fell behind third baseman Adonis Garcia. Ellsbury moved to third on Brett Gardner's grounder and scored on Wisler's wild pitch to Chase Headley.
Wisler didn't allow another run until the seventh. He was pulled after allowing back-to-back doubles to Headley and Didi Gregorius that pushed the lead to 2-0.
Braves shortstop Andrelton Simmons' acrobatic tag on Ellsbury, who was trying to steal second base, ended the fifth.
Gardner struck out as Ellsbury broke for second. Catcher Christian Bethancourt's throw pulled Simmons to the first base side of the bag, but while in the air he reached down to make the tag.
Atlanta right-hander Williams Perez, who gave up eight runs in the 15-4 loss to the Yankees on Friday night, was optioned to Triple-A Gwinnett before the game. The team recalled right-hander Jake Brigham from the minors.
Gonzalez joked that outfielder Jonny Gomes, who pitched the ninth inning on Friday night, could be an option to fill the open spot in the rotation. "We're going to stretch him out a little bit," Gonzalez said with a smile.
Gonzalez said he didn't like using a position player on the mound. Gomes was the Braves' first position player to pitch in a game since catcher John Russell on June 25, 1989, against Houston.
"It had been 26 years and I hope it's another 26 years," Gonzalez said.
Yankees: Girardi says he hopes 1B Mark Teixeira (bruised right shin) can play when the Yankees visit Boston for a three-game series that begins on Monday. "I can't really tell you because I think we all felt that he'd be playing by now," Girardi said. "Obviously it's not healing as quickly as we thought so it's really a guess for me. We just wait and see."
Yankees: RHP Nathan Eovaldi will look for his ninth straight win when the series concludes on Sunday. His streak of eight straight wins includes six on the road. He is 13-2 overall.
Braves: RHP Julio Teheran, coming off a home win over Colorado, will try to improve his 7-1 mark in 13 starts at Turner Field. Teheran is 9-6 overall and has never faced the Yankees.
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