KISSIMMEE, Fla. -- The competition for the fifth spot in the Astros' starting rotation continued to develop on two fronts Thursday.

Left-hander Zach Duke started against the Blue Jays at Osceola County Stadium. He gave up four runs in his first two innings, but also pitched out of a second-and-third-no-outs jam in the fourth while striking out five.

Meanwhile, at the Minor League complex, right-hander Jordan Lyles pitched five scoreless innings of a Triple-A game against the Nationals, allowing just two hits while walking one and striking out seven.

Manager Brad Mills said there was no significance to who pitched where.

"The guys we send over [to the complex] are going to get plenty of opportunities in the big league game," Mills said.

The other pitcher in the mix, right-hander Kyle Weiland, hasn't allowed a run in eight innings pitched this spring.

Lyles was most happy with the progression of his curveball, which he said he threw more than he ever has in a game before.

"I'm really excited about this curveball going forward. That's what I've been waiting for. I really haven't had a fourth pitch like that to go to," Lyles said.

"That fourth pitch I can go to is just a confidence-builder. I know that's what they've been waiting for. It's what we've been practicing. I think people are excited. I'm excited. I think it's the next step forward and it's going to be crucial for me."

Duke said he'll focus on the pluses that came from his outing.

"I tend to look at the positive and try to forget the negative stuff. I'm going to look at the fact that, obviously, I'm doing something better than I've done in the past, since I had five strikeouts. So I feel like my stuff is coming along. Now it's just a matter of getting the consistency for each inning," Duke said.

"Obviously, the results weren't great. "A little mixed. There were times I felt very good about it, other times where I feel like I maybe could have done a little better. It's certainly not for lack of effort."

Clemens optioned to Triple-A

KISSIMMEE, Fla. -- The Astros' second round of cuts Thursday morning included at least two players the organization still has high hopes for.

Right-hander Paul Clemens was optioned to Triple-A a day after tossing four shutout innings against the Cardinals in Jupiter, Fla., and first baseman Jonathan Singleton was reassigned to the Minor League camp.

Singleton was part of the trade that sent Hunter Pence to the Phillies last July.

General manager Jeff Luhnow and manager Brad Mills both stressed that the 21-year-old Clemens was being sent out only to be sure he gets the innings he needs to prepare for the season.

"He has a bright future in this organization," Luhnow said. "He impressed everybody [Wednesday]. I was sitting with the Cardinals' scouts and they were asking a lot of questions about him. There were a lot of wows."

Mills noted that Singleton, too, had been as good as advertised.

"I was extremely impressed with him in instructional league when I came down after the season," Mills said. "I saw how he played first base, I saw how he swung the bat, I saw his athleticism. And he did nothing but raise my opinion of him, how he performed here. No matter who he stepped in against, he had some good at-bats."

Right-hander Juan Abreu was also optioned. Reassigned were outfielders Jake Goebbert and Brandon Barnes, infielder Diory Hernandez, catchers Chris Wallace and Rene Garcia and right-hander Lance Pendleton.

The Astros now have 49 players in camp, including all members of the 40-man roster.

Worth noting

• Brett Myers, who is being converted from starter to closer, pitched his first shutout inning of the spring. In each of four previous outings, he had allowed at last one run. This is the first time Myers has worked as a reliever in Spring Training. In 2007, when he saved 27 games for the Phillies, he didn't move into the bullpen until after the regular season began.

• Minor League right-hander Angel Heredia has been suspended 50 games for testing positive for performance-enhancing substances. He's currently on the roster of the Dominican Summer League Astros.