"I thought I was out, I really thought so," Montero said.
"I was thinking I would move the runner over, because it was a lazy fly ball. Then I just see him keep running and running and I'm thinking 'Where the heck was he playing at?'
"Unfortunately, he got a little hurt, but fortunately for me I got that double. I'll take it."
One inning later, after grounding out to end a 1-for-2 night with a walk, Quentin was replaced in left field by Chris Denorfia.
"It got worn down there a little bit," Quentin said. "I was on the bases and then I had some trouble in the outfield."
Earlier Wednesday, the Padres shut down starting pitcher Andrew Cashner due to soreness in a tendon located under his right armpit. There's no telling if the Padres will do the same thing with Quentin, who had arthroscopic surgery on the knee in March and missed the first 49 games of the season.
At this point, Quentin wants to play, even if there are only 13 games remaining in the regular season.
"I'm not discouraged," he said. "It hasn't recovered as fast as it did after the surgery. My main focus will be trying to contribute."
To this point, the Padres haven't seriously discussed shutting Quentin down, because his singular focus has been on getting back on the field.
"He wants to play," said Padres manager Bud Black. "He was a little uncomfortable as the game wore on with the knee and I took him out. It just didn't feel good."
With and without Quentin, the Padres (71-78) have struggled in the first two games of this series.
They were 1-for-7 with runners in scoring position in a 3-2 setback on Tuesday and weren't a lot better on Wednesday, when they hit into three double plays and had just seven hits.
"They bunched their hits together and we didn't," Black said.
Black was alluding to the D-backs' three-run fifth inning, when Adam Eaton had an RBI triple and Paul Goldschmidt added an RBI double. San Diego starting pitcher Edinson Volquez balked in a run, as well.
"A bad inning," Volquez said. "I was in control the whole game and then one bad inning."
Volquez (10-11) allowed four runs on eight hits with no walks and five strikeouts in six innings. This was not only the first time he hadn't walked a batter all season, but it was the first time he hadn't done so as a starting pitcher since Sept. 25, 2006, when he was a rookie with the Rangers.
"About time," Volquez said of the walk-free game.
Volquez's counterpart, Trevor Cahill, ran up a high pitch count, due in part to four walks in six innings. Still, Cahill (12-11) allowed two runs on five hits with four strikeouts.
The Padres scored both of their runs in the fourth inning. After Cahill issued two walks, he allowed consecutive RBI singles with two outs to Will Venable and John Baker.
"I saw everything that at-bat. I got a good change, a good sinker. He's tough," Venable said. "The ball doesn't come straight out his hand. You've got to be patient and get a good one to hit."