Grandal busted open a close game with a three-run shot off Dominic Leone in the sixth inning, and Seager added his shot against Steve Hathaway in the seventh, the latter a rude greeting for the pitcher's major league debut.
The home runs continued a trend over the weekend, of the Dodgers bludgeoning the Diamondbacks bullpen with a meat tenderizer. LA scored 16 runs (15 earned) on 20 hits in 7⅔ innings against Arizona relievers over the weekend, including six home runs.
For Grandal, it ended a stellar July that saw him hit eight home runs, and on the season is tied for the MLB lead with 15 home runs as a catcher. He was 3-for-4 with a walk on Sunday.
Since the start of 2015, Grandal has nine three-run home runs, three more than anyone else (Justin Turner) on the team.
The home run was Seager's first of the month, but after his seventh three-hit game of the season the shortstop still hit .347 (33-for-95) with 10 doubles.
Yasiel Puig, starting for the first time in nine games, had a three-hit game of his own, including two doubles and two RBI.
Joc Pederson, who didn't even start on Sunday, added a two-run pinch-hit home run of his own to close out the scoring, his third straight day with a home run.
Muscle tightness in his back forced starter Bud Norris out after just two batters, and after that, much like the only acceptable way to consume eggs, the Dodgers had to scramble to fill several innings.
Ross Stripling was first up, entering the game at literally a moment's notice. He allowed an inherited runner to score in the first inning, but then retired nine straight batters into the fourth. Stripling ended up finishing the fourth inning, going 3⅔ innings while allowing two runs of his own.
The Diamondbacks' two-run rally in the fourth was an odd one, aided by a wild pitch from Stripling, one that bounced up and got lodged behind Grandal's chest protector. Runners were at the corners, but Jake Lamb was allowed to score on the wild catch thanks to MLB rule 5.06(c)(7), which states, "[If] a pitched ball lodges in the umpire's or catcher's mask or paraphernalia, and remains out of play, runners advance one base."
But that wasn't the only odd run of the fourth inning. The Dodgers loaded the bases in the bottom of the inning with nobody out, thanks in large part to a botched double play ball by Lamb at third base. They scored one run on a 60-foot single up the third base line by Chris Taylor, then added another on a double play by pinch-hitter Adrian Gonzalez, this one converted.
A single by Howie Kendrick tied the score, giving the Dodgers a reset of sorts on the game.
Louis Coleman pitched 1⅓ scoreless innings with three strikeouts to earn the win.
The trade deadline, which comes Monday at 1 p.m. PT. But after that, the Dodgers have a three-game series in Denver beginning Tuesday night. Brandon McCarthy starts the series opener, a 5:40 p.m. start, while the Rockies will send Jon Gray to the mound.
Home runs: Yasmani Grandal (15), Corey Seager (18), Joc Pederson (16)
WP - Louis Coleman (2-1): 1⅓ IP, 1 walk, 3 strikeouts
LP - Patrick Corbin (4-10): 5⅓ IP, 8 hits, 6 runs (3 earned), 3 walks, 6 strikeouts