Campbell delivered, putting New York ahead with his two-run single in the seventh, and a stagnant Mets lineup finally came through with several clutch hits to back deGrom in a 7-2 win over the Nationals.
"You're behind by a run and you've got runners on second and third, and the pitcher's up -- you've got to pinch hit," Collins said. "I know Jake had two more innings easily."
After going 4 for 72 with runners in scoring position over their previous nine games, the Mets were 5 for 15 this time.
"We obviously need to score more runs and hit better with guys in scoring position, and we did that today," Campbell said.
Fresh off his dominant display in the All-Star Game a week ago, deGrom (10-6) allowed two runs and three hits in surpassing his win total from last season. The 2014 NL Rookie of the Year whiffed three American League batters on 10 pitches last Tuesday in Cincinnati.
This time, deGrom struck out eight without a walk to beat the division-rival Nationals for the first time in four tries. He was pulled after only 82 pitches.
"That's not really my decision," deGrom replied when asked if he said anything to Collins about being removed. "That's their decision ultimately and it ended up working out for the best."
Wilson Ramos hit a two-run homer for Washington, which leads the NL East by two games over the Mets.
Rookie starter Joe Ross (2-2) gave up three runs -- two earned -- and four hits in 6 1/3 innings.
Flores singled to open the seventh. Nieuwenhuis followed with a bouncer up the first base line that deflected off Clint Robinson's glove and into foul territory for an error, putting runners on second and third.
"He's had, in my opinion, the best at-bats in the last two or three games and so I just said, `I think he's the guy to go up there," Collins said.
The 22-year-old Ross was filling in for injured Stephen Strasburg and beginning his second stint with Washington.
"He was in command the whole time he was out there," manager Matt Williams said. "Got up there in pitches, and had some trouble there in the last inning. But I thought he pitched great."
Ross retired his first nine batters before the Mets got to him in the fourth.
Granderson led off with a single and stole second. He moved to third on a groundout and scored on a single by Flores, who had two RBI.
After deGrom faced the minimum through four, Yunel Escobar doubled to open the fifth. With two outs, Ramos drove a 1-0 fastball just over the wall in right for his ninth homer of the season.
Mets: LF Michael Cuddyer was out of the starting lineup for the second straight night with a sore left knee. He walked as a pinch hitter in the ninth and scored.
Nationals: Strasburg (left oblique strain) threw his first bullpen session since going on the disabled list July 5. Williams said Strasburg threw about 30 pitches and had no issues. ... INF Anthony Rendon (left quad strain) went 1 for 3 with two walks in his third rehab game with Class A Potomac.
Washington right-hander Abel de los Santos made his major league debut, getting the final two outs in the ninth. "Just aggressive and he threw the ball over the plate," Williams said.
Collins acknowledged that deGrom, who entered with a .205 batting average, is no slouch at the plate. "No disrespect to Jake deGrom -- he does handle the bat," Collins said. "(But) he's not a position player. There's a reason why they took him off shortstop (in college) and made him a pitcher."
Mets rookie Noah Syndergaard (4-5, 3.05 ERA) makes his 13th start Wednesday afternoon in the series finale. Syndergaard is 2-1 with a 1.55 ERA over his last four starts. He'll oppose Jordan Zimmermann (8-5, 3.27), who hasn't lost since June 17. He's 3-0 with a 1.99 ERA since that defeat.