DENVER — Rockies right-hander Jon Gray mixes a 96-mile-per-hour fastball, a 90 mph slider and an 81 mph curveball. When he's in a groove, it's a lethal combination.

Why, then, does Gray have a 1-3 record, with a 6.23 ERA, .311 batting average against and a 1.52 WHIP (walks plus hits per inning pitched) this season? Why will he take the mound against the Cubs tonight at Coors Field still searching for answers in a season when he was projected to the Rockies' ace?

Because, at age 26, with 62 big-league starts under his belt, and despite his enormous talent, he remains a work in progress. That does not rest easy with Gray.

"I can't stress how frustrating it is to go out there and cruise and then let it all go to waste," Gray said after the Rockies' 6-2 loss to the Nationals last weekend when he didn't make it out of the sixth inning.

Through the first five innings, Gray was on the money, allowing just one run on three hits while striking out six. He was holding his own against Max Scherzer, the three-time Cy Young Award winner. But then Gray gave up back-to-back singles to Wilmer Difo and Bryce Harper to open the sixth, prompting manager Bud Black to come out and give Gray a pep talk — and issue him a challenge to get the job done.

But the Nationals kept their rally going with an RBI single, a run-scoring squeeze bunt and a two-run double, turning a 2-1 Rockies lead into a 5-2 deficit.

"I can be good 95 percent of the time but not good five percent of the time. It doesn't matter, I guess," an emotional Gray said. "I've got to find a way to be good right there."

Black agreed, saying that Gray must figure out a way to take the next step.

"He matched (Scherzer)," Black said. "But these types of games are learning experiences for Jon and other pitchers who match up against these types of great pitchers. When you go up against a guy like Scherzer, man, you've got to be on your game. And Jon was on it for five innings, and then the ball climbed up a little bit."

Although it's early in the season, a trend has emerged. Opponents are hitting .524 with a 1.345 OPS in their third at-bat vs. Gray. There is no denying Gray's raw talent, which is why he was the third overall pick in the 2013 draft.

"He has really good stuff. Great stuff, in fact," said a major league scout who has frequently watched Gray pitch. "Look what he did against (Paul) Goldschmidt last year. He made "Goldy' look bad, and that doesn't happen very often."

Last season, Arizona's All-Star first baseman was 0-for-11 with five strikeouts against Gray, until the first inning of the wild-card playoff game at Chase Field when Goldschmidt clobbered Gray's first-pitch, a hanging curveball, for a three-run homer. The Diamondbacks won the game 11-8 and left Gray searching for answers.

When Black visited the mound at Nationals Park last Saturday, he had a message for Gray, who took it to heart.

"We talked about times in the game, when a starter get a few guys on, that's when you have to bear down and make pitches," Gray said. "We talked about that all week, and that's part of the reason I'm so frustrated right now. I've been waiting for that time and I didn't make the pitches I wanted to."