Kelly is taking Jason Marquis' spot in the rotation. Marquis is on the 15-day disabled list with a broken left wrist. Kelly himself has been injured this season, missing four months with a strained right elbow. But Kelly is now healthy and he will be looking to help the Padres extend their seven-game winning streak.
Manager Bud Black said he is looking forward to the 22-year-old's debut, even as he tries to downplay expectations.
"There are Major League debuts across the landscape of our game, almost daily sometimes," Black said Sunday. "With Casey, it's a little different. He's more of a higher-profile guy but I don't want to put too much weight on tomorrow's game just because it's unfair for a lot of reasons. We saw it here in Arizona when Trevor Bauer made his debut. It's one game."
Bauer, the D-backs' top prospect, also debuted against the Braves, allowing two runs in four innings June 27 in Atlanta. After four subpar starts, he was sent back to Triple-A to continue to develop.
While Monday is a day of celebration for Padres fans who have waited patiently for Kelly's arrival, it is just another day in the pennant race for the Braves. They hold one of the National League Wild Card spots and trail the Nationals by 4 1/2 games in the NL East.
Left-hander Paul Maholm will start for the Braves. It will be his second start against the Padres in 12 days. He allowed one run in seven innings as Atlanta beat San Diego, 6-1, on Aug. 15. Maholm picked up the win, setting a career high with 11.
Maholm was acquired by the Braves in a trade with the Cubs on July 30 and said he is enjoying being a part of Atlanta's playoff push.
"When you've got a club that's playing well, it's fun to come in every day and it's fun to go out there for your start days," Maholm said. "You've just got to make sure you keep us in it and let the offense get relaxed and put up some runs."
Braves: Jones remains sidelined with sore oblique
Chipper Jones was out of the Braves' lineup for the second consecutive day Sunday with a sore left oblique. He did pinch-hit in the eighth Sunday night, grounding out to end the inning. Before the game, Jones said he hoped the problem would clear itself up with a day or two more of rest.
"It's not anything that will keep me out a week or two as long as I am smart with it," Jones said.
Jones is playing his last season before retirement. This series will be his final one against the Padres. In 129 games against the Padres in his career, Jones has hit .316 with a .558 slugging percentage.
Right fielder Jason Heyward stole his 19th base in the Braves' 7-1 victory Sunday night. He is now just one stolen base shy of being the first Braves player to hit 20 home runs and steal 20 bases in a season since Andruw Jones in 2000.
Heyward is hitting .279 with 24 home runs this season.
Padres: Streaking to the finish
With their 5-4 victory against the D-backs on Sunday, the Padres extended their winning streak to seven games. It is their longest winning streak since April 2010, when they won eight games in a row.
Though the Padres were one of the worst teams in the Major Leagues the first two months of the season, they have been one of the best since June 8. Since that day, the Padres are 40-30, which is tied with the Braves for the fourth-best record in the National League.
Reliever Dale Thayer will return from the paternity leave list for Monday's game. Thayer missed all of the Padres' series against the D-backs over the weekend.
Thayer has seven saves and a 3.89 ERA in 44 innings this season.
The Padres scored their lone run off Maholm on Aug. 15 thanks to a home run by Logan Forsythe. He went 2-for-4 in the game.