Johnson broke his right leg in an outfield collision during the eighth inning of the New York Mets' 12-6 victory over the Nationals on Saturday.
The first baseman collided with right fielder Austin Kearns while chasing David Wright's blooper down the right-field line that fell in for a triple. Johnson was immobilized and taken to a hospital. He was scheduled to have surgery Saturday night in New York to repair his right femur, the bone in the upper part of his leg.
Second baseman Jose Vidro, who was near the collision, said he heard a "crack." Washington manager Frank Robinson said that when trainers tried to move Johnson, "You can't even describe the sounds he made."
"You sit there and see a teammate and a friend on the ground yelling in pain," Kearns said. "It makes you sick to your stomach. I'm just sick to my stomach, I don't know anything else to say."
The oft-injured Johnson actually remained healthy nearly all season. He batted .290 with 23 homers, 77 RBI and 110 walks in 147 games.
"Obviously, he was in pain. You just hate to see it happen," said Wright, who went out into the outfield to check on Johnson.
"You have two competitors out there, two big bodies out there going full speed on each other. The Carlos Beltran and the Mike Cameron collision and now this one. Two people just playing the game hard."
Said Beltran, who is out with a strained quadriceps: "I feel sorry for him, he's a good guy."
Earlier, Wright's three-run homer capped a six-run fifth inning, helping the Mets erase a 4-0 deficit.
Paul Lo Duca also homered and Wright finished with three hits and three runs for the Mets, who snapped a three-game skid. Jose Reyes drove in three runs and reached base five times with a two-run double, an RBI single, another single and a pair of walks.
The Mets broke open the game with three runs in the seventh and three more in the eighth.
John Maine (6-5) got the win despite throwing 110 pitches in five innings. He allowed four runs and three hits, struck out seven, walked five and hit two batters with pitches.
Alfonso Soriano hit his 46th homer for the Nationals. Michael O'Connor (3-8) yielded six runs and eight hits in 4 2/3 innings.
Shawn Green led off the fifth with a double and scored on a single by Lastings Milledge. Chris Woodward's double put runners at second and third, and after pinch-hitter Jose Valentin struck out, Reyes and Endy Chavez followed with consecutive RBI singles to bring the Mets to 4-3.
O'Connor got Lo Duca to fly out, but Wright followed with his 25th homer to give New York a 6-4 lead. Julio Franco and Green followed with singles off Ryan Wagner before Milledge flied out to end the inning -- after the Mets had eight hits by seven players.
"We had been a little stagnant last couple of days," said Mets manager Willie Randolph, who began his postgame remarks by asking reporters to pray for Johnson. "That happens, that's the way baseball is. Guys were a little more aggressive today, taking advantage of some of the momentum we had."
Soriano homered in the seventh, but the Mets answered with Woodward's RBI single and a two-run double by Reyes to make it 9-5. Lo Duca hit his fifth homer in the eighth before Franco and Milledge added run-scoring doubles.
Maine, hoping a strong start could help land him a postseason role, cruised through the first three innings before losing his control and needing 68 pitches to get through the next two.
The Mets had two hits in the first but didn't score in part because of a brilliant double play started by Nationals catcher Brian Schneider. With the speedy Reyes at first, Schneider ran back to make a diving catch of Chavez's fouled bunt attempt, then made a long throw to second to nail Reyes, who had tried to tag up.
Lo Duca (thumb) was back in the lineup after missing two games, but it will be at least another day before Beltran returns. Beltran and Randolph said the CF would see how he felt Sunday, but Beltran seemed to indicate that he might not play until the series finale Monday night . ... The Nationals were without pitching coach Randy St. Claire, who had the flu. Robinson made all the visits to the mound.