PHOENIX -- The D-backs felt like they entered Game 5 of the National League Championship Series on Saturday in strong position to head back to Philadelphia with the upper hand in the series.

It wasn’t just because their momentum was at an all-time high with back-to-back wins in Games 3 and 4. Or because they had the roar of a sellout crowd behind them.

It was because Zac Gallen, their ace and the National League starting pitcher in this summer’s All-Star Game, was taking the mound.

But just like in Game 1, the Phillies tormented Gallen. The right-hander gave up four earned runs, two coming off homers, and struck out just one batter in Arizona’s 6-1 loss at Chase Field.

It was Gallen's 119th career start (including the postseason) and the first time he did not record multiple strikeouts.

“I think they’re just a good lineup, really,” Gallen said. “And they capitalize on the mistakes that I made. I think sometimes as a pitcher, [you can] get away with some early mistakes. And that's a team that doesn’t really miss mistakes.

“As a pitcher, you're going to make mistakes. You just try to minimize them and hope, like I said, the ones you do make that you get lucky with.”

Gallen was greeted by Kyle Schwarber, who had just become the all-time left-handed postseason home run leader on Friday. But it was an opposite-field slow roller that traveled five feet that got him on base to open the game. Four batters later, Bryson Stott drove in Schwarber with a single.

Before Gallen could get out of the inning, the Phillies pulled off a double steal that resulted in Harper scoring from third while colliding with D-backs catcher Gabriel Moreno.

Just like that, the D-backs trailed by two runs before coming to the plate.

“I think Zac had good stuff that first inning,” D-backs manager Torey Lovullo said. “With that infield base hit, it wasn't what we were at all expecting.”

After issuing a walk to Nick Castellanos in the second inning, Gallen settled in to retire 11 straight batters. That streak ended in the sixth when he faced the order for the third time.

Schwarber made him pay for leaving a hanging knuckle curveball down the middle of the plate, sending the ball a Statcast-projected 461 feet to right-center field for a home run. Two batters later, Harper went deep, putting the D-backs in a 4-0 deficit.

“I thought Zac threw the ball well enough,” Lovullo said. “He just made some mistakes in the last inning of work, and that score went from 2-0 to 4-0 real quick, and that's what can happen when you do make some mistakes.”

Gallen threw the second-most innings in MLB during the 2023 regular season, and entering Saturday, he had 226 1/3 innings overall. But after the D-backs had a bullpen game on Friday, they needed Gallen to pitch as deep as he could.

“Do I feel like he is fatigued? I don't think so,” Lovullo said. “He will never tell me he is. He wants the baseball. He wanted to go back out there for the seventh inning. He did not want to come out of this game. And I told him, ‘You did your job. It's time to turn it over to the bullpen.’”

The D-backs will hop on a flight to Philadelphia on Sunday morning. Merrill Kelly, who gave up four earned runs in 5 2/3 innings in Game 2, will pitch with Arizona’s season on the line. Teams ahead 3-2 in previous best-of-seven postseason series have advanced 71 percent of the time.

“This team is resilient,” Gallen said. “I don't think anyone thought this was going to be an easy task. For this series and anything going forward, really, I have faith in the guys.

“It’s pretty bumming on my part. They grind, they do what they can and I just didn't give them a chance, really, tonight.”