Acquired in an offseason trade, Mazzaro struggled Saturday in the Royals' 10-9 loss to the Colorado Rockies. He gave up four runs and five hits in 1 1/3 innings.
Mazzaro is trying to fill a vacancy in the Royals' rotation. He retired the first two batters before yielding three runs on four hits, giving up consecutive doubles to Carlos Gonzalez and Jason Giambi.
"The first two batters went pretty quick then I just found too much of the zone with my fastball," Mazzaro said. "I could have made better pitch selection. Overall, I was happy with the offspeed pitches that I was throwing. The slider, curveball and changeup were really good. My fastball command was a little shaky."
Gonzalez went 3 for 3, scored twice and drove in a run. He was the NL batting champion last year at .336.
Giambi doubled twice and had two RBIs. Kila Ka'aihue homered for the Royals.
The Royals acquired Mazzaro in a Nov. 10 trade for outfielder David DeJesus. The Kansas City newcomer threw 50 pitches, 31 for strikes.
"With 50 pitches, I should have been in at least the fourth or fifth inning," he said. "I got my work in and I'm feeling good."
"I'm happy to be here. I think it was a great trade for me personally. I'm excited. Coming to a new ball team, new eyes on you, you want to impress guys."
Will Smith, a 21-year-old left-hander who has never pitched in the majors, retired all six batters he faced after Mazzaro left. Smith has been flawless in his first two appearances.
"It's hard to beat nine up, nine down," Smith said. "If it stays like this, I'll be happy."
Esmil Rogers, who is competing for a Rockies' rotation job, allowed four runs. He gave up four hits, walked two and hit two batters in three innings.
"I felt great," Rogers said. "If you have confidence in yourself, you're going to be great in the games. Sometimes you have to make your pitches. That's what happened today. I moved my back a little, and that's why I hit a couple hitters and threw a couple walks. Sometimes I want to do more than I can."
Royals C Jason Kendall caught bullpen sessions for the first time since major shoulder surgery in September. He also has begun to take batting practice swings and is throwing up to 90 feet. "I went out to see him take batting practice and all I needed to see was five swings," KC manager Ned Yost said. "He was hitting line drives all over the park. He's progressing, way, way ahead of schedule." ... Rockies manager Jim Tracy was not with the team. He attended the funeral of his friend Jenny Colborn, wife of Jim Colborn, who was a pitching coach under Tracy when he managed the Dodgers. Tracy is scheduled to rejoin the Rockies on Sunday. Bench coach Tom Runnells ran the team in Tracy's absence.