WASHINGTON -- Dusty Baker is big on numbers and milestones, and he wants to see ace pitcher Max Scherzer try and win 20 games this year.

But Baker needed to pinch-hit for Scherzer in the sixth inning Tuesday night with his team trailing 2-0.

The Washington manager got the best of both worlds as the Nationals scored four runs in the sixth and Scherzer got his 19th win of the year when the Nationals came back to beat the Arizona Diamondbacks 4-2 despite being held to three hits. The Nationals have won the Scherzer's last nine starts.

"Dusty was out of his mind," Scherzer said with a grin, after the Nationals took the lead in the sixth. "That is what made it fun. We were both pumped up."

Anthony Rendon hit a go-ahead three-run homer in the sixth inning after Scherzer was lifted for pinch-hitter Wilmer Difo earlier in the frame.

"He went down and got it," Arizona manager Chip Hale said of the homer.

Jose Lobaton, starting in place of injured catcher Wilson Ramos, had the first hit for the Nationals when he blooped a single to center to start the sixth off Arizona starter Matt Koch. His five hitless innings were the most for an Arizona pitcher in his first career start, as he threw 69 pitches.

"He was around the zone," said Hale. "He goes right after guys. It was good to see. He showed us he can do it. He had a little blister issue that cropped up at the end. That is not the reason he came out. He had a win in his pocket and it went away quick. His ball moves. He is around the zone. He elevated when he had to. It was a very impressive outing."

After a walk to pinch-hitter Wilmer Difo, Koch was replaced by Randall Delgado. Trea Turner walked to load the bases and two batters later Stephen Drew drove in a run with a sacrifice fly to make it 2-1.

Rendon then golfed a pitch from losing pitcher Delgado (4-2) over the fence in left to give Washington a 4-2 lead. It was the 19th homer of the year and 500th career hit for Rendon, a former first-round pick out of Rice. That gave Rendon 84 RBIs this year, a career-best, after he had just one RBI in April.

"Randall comes in and gives up another walk," Hale said. "It is something we are going to have to fix. It is happening too many times. For me it is more about the walks."

Koch, in his first career start, gave up just one hit and two runs in five innings and did not figure in the decision. Delgado yielded two runs on the one hit in one inning.

Scherzer (19-7) has one more start left this weekend. He gave up six hits and two runs with two walks and 10 strikeouts. Scherzer now has 277 strikeouts this season, the most in Nationals history, from 2005 to present. He said Arizona went after his fastball early in the count so he had to change his approach.

"He went to his slider and he went to his changeup," Baker said of Scherzer.

Sammy Solis pitched a perfect seventh for the Nationals and Shawn Kelley went a scoreless eighth. Closer Mark Melancon got his 14th save for Washington and 44th overall as he threw the ninth, getting University of Virginia product Phil Gosselin for the last out on a bunt pop to Rendon at third.

Chris Owings had two hits for the Diamondbacks.

The Nationals (92-65) are now 14-17 against the National League West this year while Arizona (65-92) has lost four of its last five.

Jean Segura hit the first pitch of the game from Scherzer over the fence in left for his 20th homer of the season. It was the 29th homer allowed this year by Scherzer, which is tied for the league lead.

"After that he settled down," Baker said of his ace.

Scherzer, after giving up five hits in the first three innings, fanned six in a row before Paul Goldschmidt drew a walk with two outs in the fifth.

NOTES: Washington C Wilson Ramos has a torn ACL in his right knee and is done for the year, manager Dusty Baker said Tuesday. Ramos was injured in the sixth inning Monday when he came down awkwardly after taking a relay throw from 1B Ryan Zimmerman. Ramos, a pending free agent, will have surgery at some point in the next week after hitting .307 with a career-high 22 homers and 80 RBIs in 131 games. "This was the most inopportune time for this to happen," Baker said. The Nationals started C Jose Lobaton (.220 in 35 games) on Tuesday and will also use C Pedro Severino, hitting .350 in 12 games ... C Spencer Kieboom was called up from Double-A Harrisburg on Tuesday by Washington to give the team more catching depth. He was already on the 40-man roster and will be making his MLB debut. He hit .230 in 94 games with Harrisburg this year ... Washington LHP Gio Gonzalez (11-10, 4.51) will face Arizona RHP Shelby Miller (2-12, 6.47) on Wednesday ... The Nationals were also without RF Bryce Harper (thumb) and INF Daniel Murphy (strained glute) in the starting lineup ... Arizona RHP Matt Koch, who made his first MLB start Tuesday, had a 1.29 ERA in five bullpen outings to begin his big league career.