The success or failure of the Colorado Rockies bullpen in 2017 may ride on the success or failure of several pitchers recovering from Tommy John surgery. One of those pitchers, Jairo Diaz, took a major step forward in his recovery on Monday, pitching in his first major league game since his surgery. Diaz had several positives in his return, but struggled as his pitch count climbed.

Diaz started strong in his first action since Spring Training last year, getting Kyle Schwarber to fly out and striking out Albert Almora Jr. His velocity was consistently above 95 MPH on his two-seam fastball and reached 99 MPH on one occasion. He ran into trouble, though, with his location as his outing wore on

“We’re going to monitor him,” Rockies manager Bud Black said postgame. “We like the way he’s throwing, as far as his ‘stuff’. You know, the velocity seems to have come back.”

After retiring the first two batters he faced, Diaz allowed the next five to reach base, all of whom would eventually score. He surrendered a first-pitch home run to Matt Szczur and walked Jeimer Candelario after starting the at-bat 0-2. He did not finish the inning after throwing 27 pitches and retiring two of the seven hitters he faced.

“You know, we’re going to continue to watch his progress as he bounces back from outings,” Black continued. “We’re going to critically evaluate his slider and his changeup, but it could be before May [that he is at full strength].

“We have two more weeks of Spring Training. He’ll get a couple more outings – whether they’re with us or on the minor league side. But just how he’s feeling and how his overall stuff is, it’s pretty good.”

Diaz tore a ligament in his right elbow in early March last year and missed the entire 2016 season. He joins Greg Holland as hard-throwing right-handers in the Rockies bullpen that missed all of last year recovering from Tommy John surgery. Adam Ottavino also missed roughly the first half of 2016 recovering from the surgery as well.

Diaz is one of Colorado’s power arms, along with Holland and Carlos Estevez, in the bullpen as the Rockies follow the MLB trend of high-velocity relievers filling roles in the sixth, seventh and eighth inning. Diaz could find himself pitching in any of those three spots should his recovery continue on time.

In 26 career games in the majors, Diaz has a 2.55 ERA and 26 strikeouts over 24.2 innings pitched. He carries a lifetime 5.26 ERA over 422.2 innings pitched in the minor leagues. Diaz came to the Rockies following the 2014 season in exchange for infielder Josh Rutledge.