The Reds' reliever struck out three straight Braves with the bases loaded and the Reds held on for a 4-2 win on Thursday night in a rain-delayed victory.
Luis Castillo shook off early problems to pitch six scoreless innings for the Reds but loaded the bases to start the seventh. Hernandez relieved and struck out Dansby Swanson, Ender Inciarte and Ozzie Albies to maintain a 3-0 lead, earning a high-five procession in the dugout.
''I came into the game thinking, 'Don't walk anybody,''' Hernandez said. ''I was just going to use fastballs and sliders, get ahead and expand the strike zone. I don't think I've ever come into a game and got three strikeouts. I've loaded them myself and got out of them, but not like this.''
''David Hernandez won this game,'' Castillo said through an interpreter. ''I thanked him before. I thank him even more now.''
Freddie Freeman hit a two-run homer for Atlanta, but the Reds held on for their second win in the three-game series.
Raisel Iglesias got the final five outs for his sixth save.
The game was delayed 2 hours, 42 minutes by rain in the middle of the seventh.
Castillo (3-1) allowed a season-high five hits over the first three innings but retired nine straight before getting into trouble in the seventh. He also got his first hit of the season and scored on Eugenio Suarez's drive off the left field wall. Suarez was thrown out at second.
''Castillo's stuff was electric,'' Atlanta catcher Brian McCann said. ''He made the pitches when he had to.''
Suarez delivered a drive to almost the exact same spot in the fifth for a two-run double.
Atlanta's Ronald Acuna Jr., the reigning NL Rookie of the Year, celebrated the first anniversary of his major league debut in Cincinnati last season by going 1 for 3 with a walk, but he was robbed twice by Suarez. The third baseman barehanded a slow bouncer behind the bag and threw Acuna out at first to end the first and made a diving stab of Acuna's sharp one-hopper to lead off the fourth.
''He's really good,'' Braves manager Brian Snitker said of Suarez. ''He's good defensively. He's a force offensively. He's just a solid, solid player.''
Julio Teheran (2-3) pitched six innings, allowing five hits and three runs with three walks and seven strikeouts against a Cincinnati offense that went into the game with a major league worst .199 batting average.. He also hit a batter.
''Suarez is the only hitter who put the barrel on the ball,'' McCann said.
Yasiel Puig fumbled his way into an outfield assist in the third. He misplayed Freeman's hit in right field but recovered in time to throw out Freeman at second base.
BEEN A WHILE
Atlanta RF Nick Markakis batted leadoff for the 324th time in his career and first since May 16, 2016. After going 1-for-4, he is hitting .291 (389-for-1339) in the leadoff slot.
THAT LOOKS GOOD
Reds LF Jesse Winker acted as if he was going to pick some food off the plate of a fan sitting in the front row after catching a foul popup in the sixth.
Jose Peraza led off the Reds' seventh with a walk. He'd gone 71 plate appearances without a walk, the most in the majors this season.
Braves: RHP Darren O'Day is scheduled to be re-evaluated Tuesday. O'Day has been out all season with a right forearm strain and still is not throwing.
Reds: LHP Alex Wood threw a bullpen Wednesday in Arizona and is scheduled to throw another Saturday. Wood has been out all season with back spasms. He will need two or three bullpen sessions before the team decides on its next move, manager David Bell said Thursday.
Braves: Atlanta hopes to improve on its 7-6 home record during a seven-game stand that opens Friday with the first of three against Colorado.
Reds: Cincinnati opens a seven-game road trip Friday with the first of three in St. Louis. They are the last seven of a stretch in which the Reds play 20 of 26 games away from Great American Ball Park.
More AP MLB: https://apnews.com/MLB and https://twitter.com/AP-Sports