Mets starter Jonathon Niese pitches during the third inning against...

Mets starter Jonathon Niese pitches during the third inning against the Philadelphia Phillies, Monday, Aug. 11, 2014, in Philadelphia. Credit: AP

Earlier this season, Jacob deGrom and Rafael Montero arrived in the big leagues on the same day. Together, the promising pitching prospects boarded a flight from Las Vegas and then strolled into the Mets' clubhouse for the first time.

DeGrom went on to become one of the top rookies in the National League, but Montero soon found himself back in the minor leagues.

Their paths had diverged until Monday, when they were linked again.

The Mets placed deGrom, 26, on the 15-day disabled list with right rotator cuff tendinitis and summoned Montero, 23, as his replacement. In his first big-league start since May, Montero will take the mound Tuesday night -- which would have been deGrom's turn to pitch -- against the Nationals.

Assistant general manager John Ricco framed deGrom's diagnosis as "good news," and manager Terry Collins said he is "very relieved."

For now, deGrom will be sidelined for only two starts. He will rest and take anti-inflammatory medication, a relatively encouraging development given that rotator-cuff injuries are considered among the most serious for pitchers.

"That's about as good as you can hope for, that that was all it was going to be," Collins said. "It's a good step for him, giving him a little down time to get some energy and strength back in his arm."

As deGrom visited with doctors in New York, the Mets held on to beat the Phillies, 5-3, thanks to a bounce-back outing by Jonathon Niese and a three-run homer by backup catcher Anthony Recker.

Niese (6-8) snapped a stretch of four consecutive losses, holding the Phillies to Darin Ruf's two-run homer in his seven innings. The Mets pushed ahead with a four-run seventh, keyed by Matt den Dekker's tying RBI double and Recker's fourth homer. He was in an 0-for-19 slump entering the at-bat.

With closer Jenrry Mejia out because of his recent workload, Jeurys Familia pitched 1 1/3 innings for the save.

Familia survived a tricky ninth inning, as pinch hitter Chase Utley appeared to hit a two-out, two-run homer that pulled the Phillies to within 5-4. But a video review showed that Utley's drive was helped over the fence by a fan leaning over the railing. He was awarded an RBI double but was stranded when Ben Revere flied out to end it.

Even as the Mets clinched a 4-3 road trip, word of deGrom's prognosis carried heavier weight than the outcome.

In May, the Mets promoted deGrom to help fill out the bullpen, with Montero slated to join the rotation. But when Dillon Gee landed on the disabled list with a back injury, deGrom joined the rotation.

Montero started four games, going 0-2 with a 5.40 ERA. By the end of May, he was on the way back to Triple-A Las Vegas, where the Mets hoped he would rediscover his command.

Meanwhile, deGrom began his surprise bid for NL Rookie of the Year.

He is 6-5 with a 2.87 ERA in 16 starts, emerging as an equal to the likes of Zack Wheeler and Noah Syndergaard.

Now the Mets can only hope that deGrom's shoulder issue turns out to be minor and that Montero fares better in his second chance in the big leagues. His brief experience in the majors -- and the fact that he's already on the 40-man roster -- helped make him the choice for a promotion over Syndergaard.

Montero was 6-3 with a 3.28 ERA with Las Vegas. He has posted a 2.12 ERA since returning from an oblique strain suffered in mid-June.

Team officials have been most encouraged by a return of Montero's sharp command, which is what initially put him on track for a promotion.

"He's got to be himself," Collins said. "And it sounds like he's back to where he was a year ago."