Bryce Harper, Kyle Schwarber and Nick Castellanos all homered to stake the Philadelphia Phillies to an early lead, and the defending National League champions held on for a 5-3 win over the Arizona Diamondbacks in Monday's Game 1 of the NL Championship Series.

The three solo homers helped back a solid six-inning start from Zack Wheeler as the Phillies handed the surprising Diamondbacks their first loss of this year's post-season. Arizona began the playoffs with five straight wins, including a three-game sweep of the NL West champion Los Angeles Dodgers in the previous round.

Harper added an RBI single on his 31st birthday to help provide Philadelphia a 5-0 lead as Wheeler held Arizona to just one hit through the first five innings.

Schwarber started the power surge by leading off the bottom of the first inning with his first homer of this postseason, and Harper made it 2-0 two batters later with his fourth homer in his last five games.

Castellanos, who homered twice in each of the final two games of Philadelphia's division series win over the Atlanta Braves, went deep again an inning afterward to pad the lead.

All three long balls came off Diamondbacks ace Zac Gallen, who surrendered all five Philadelphia runs and eight hits over five innings.

The Phillies increased the margin when Trea Turner doubled in the third and scored on Harper's single, and the lead grew to 5-0 when Harper walked in the fifth and later came home on J.T. Realmuto's two-out single.

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Wheeler, meanwhile, retired 15 straight Arizona hitters after permitting a single to Corbin Carroll to open the game. That streak ended when Evan Longoria led off the sixth with a single and Geraldo Perdomo followed with a two-run homer to get the Diamondbacks on the board.

The Phillies ace finished with eight strikeouts and yielded just three hits along with the two runs.

Seranthony Dominguez relieved Wheeler in the seventh and committed an error that led to an unearned run which brought Arizona within 5-3, but Jose Alvarado and Craig Kimbrel held the Diamondbacks scoreless over the final 2 1/3 innings.

Game 2 will take place Tuesday in Philadelphia, with the Phillies sending out Aaron Nola and Merrill Kelly getting the call for the Diamondbacks.