CHICAGO -- It was an open secret, shrouded in mystery, with no when or where. But there is finally clarity. Right-hander Peter Lambert, 22, the Rockies’ No. 4 prospect according to MLB Pipeline, made his Major League debut Thursday afternoon in the series finale against the Cubs at Wrigley Field, earning the win in the club's 3-1 victory. He made franchise history by becoming the first Colorado pitcher to strike out at least nine batters in his big league debut, while also notching his first hit on the first pitch that he saw as a batter.

After lefty Kyle Freeland was optioned to Triple-A Albuquerque last week, the Rockies were down to four starters and in need of a fifth, and they were discussing when to call up Lambert (2-2, 5.07 ERA in 11 starts at Albuquerque). Finally, they decided to give righty Jon Gray, originally scheduled for Thursday, extra time because he has been dealing with a “hot spot” on his right middle finger for two starts. Gray will pitch Saturday’s second game against the Mets at Citi Field, with righty Antonio Senzatela going in Friday's series opener.

So Lambert received word Tuesday, with Albuquerque playing at Omaha, and was at Wrigley on Wednesday, shagging balls during early batting practice and trying to overcome the wonder of being in a baseball cathedral so he can pitch with a clear mind Thursday.

“I’m super excited -- this place is pretty unbelievable,” said Lambert, who was placed on the “taxi squad,” which means the Rockies didn’t have to make moves to put him on the 25-man active roster and the 40-man Major League roster until before Thursday’s game.

It has been a somewhat speedy route to the Major Leagues for Lambert, the Rockies' second-round pick in the 2015 MLB Draft out of San Dimas (Calif.) High School. At the time thin and not overpowering, Lambert came to pro ball ahead of other hard throwers with his secondary pitches. But he took off in the Minors by sharpening his fastball.

In his last three starts, Lambert had 20 strikeouts against just one walk. The buzz grew louder on May 24, when he struck out 10 in seven innings against Las Vegas -- on a night when his fastball allowed his changeup to come into play. The next day, Freeland, a Cy Young Award candidate last year, lasted four innings against the Orioles and only three innings in his next start vs. the D-backs. The day after that, Freeland was sent down.

“I’ve done well in Albuquerque this year, had a few good ones and a few bad ones, but my fastball command is pretty good right now,” Lambert said. “That’s the biggest part of my game. If my fastball command is good, everything plays off that.”

Lambert played the waiting game. His callup became clear when he was scratched from a scheduled start at Omaha on Tuesday night.

Lambert has been in Major League camp the last two years and made his first Cactus League start this year, against the Royals. During the spring, right-hander Chad Bettis spent time lending his experience. On Wednesday, after Lambert arrived, he listened to teammates tell him of their debuts. But with help from catcher Tony Wolters, he also began studying to face players who used to be famous dudes on TV. Thursday, they were his opponents.

“Tony already came up to me and gave me some information on it,” Lambert said. “It gives me a ton of confidence knowing that they’re here to help me as much as they can.”

Left-hander Mike Dunn was placed on the 10-day injured list on Thursday, retroactive to Monday, due to left a/c joint inflammation.

Injury updates

• Right fielder Charlie Blackmon has joined the Albuquerque squad in Omaha to begin his Minor League rehab assignment for a right calf injury that, by Wednesday, had cost him his 12th game.

• Closer Wade Davis pitched a simulated game at Wrigley on Wednesday and reported feeling good. Davis had a left oblique strain, but with that calmed down, the key is making sure the arm is fine. He has had no problems in bullpen sessions in the days leading up to the simulated game.