The 50-year-old Clemens signed with the Skeeters of the independent Atlantic League on Monday and he is expected to start for the minor league team on Saturday at home against Bridgeport.
"His fastball was clocked at 87 mph. All of his pitches were working," said Randy Hendricks, Clemens' agent. "He threw a three-inning simulated game after an extensive workout warmup."
Clemens and Skeeters manager Gary Gaetti have been talking about this "for months," Hendricks said. Clemens is expected to discuss his decision Tuesday during a news conference in Sugar Land, about 20 miles southwest of Houston.
Clemens, acquitted in June of charges he lied to Congress when he denied using performance-enhancing drugs, hasn't played for a team since pitching for the New York Yankees in 2007 at the age of 45. He went 6-6 in 18 games with a 4.18 ERA that season.
Texas Rangers pitcher Roy Oswalt, a former teammate of Clemens with the Astros, is excited about his friend's return to baseball.
"I think he's going to show everybody that all that stuff that he had to go through had nothing to do with the success he had in the big leagues," Oswalt said. "He said he's going to do it a little bit and see how his body responds. I wouldn't be surprised next year if he's pitching in the big leagues for somebody."
Clemens has been throwing batting practice to one of his sons often, and Oswalt said that Clemens "feels pretty good."
Yankees manager Joe Girardi, who is three years younger than Clemens, said it is difficult to get that urge to compete out of your blood.
"He's always loved to compete," Girardi said of Clemens. "That's who he is. He kept coming back. There were times he felt he couldn't quite go a full season, but he gave it as much as he had. He loved to compete. That's a hard thing to replace is that competition. Guys miss it."
Clemens had two great seasons with the Astros after he turned 40, going 18-4 with a 2.98 ERA in 2004 to win his record seventh Cy Young Award. He was 13-8 with a career-low 1.87 ERA in 2005.
Clemens earned $160 million and won 354 games in a 24-year career with the Red Sox, Yankees, Blue Jays and Astros. His 4,672 strikeouts are third-most and he was named to 11 All-Star games.
Now he will see what he has left for the Skeeters, who play in the Atlantic League. He joins a roster that includes former major league pitchers Tim Redding and Scott Kazmir and Jason Lane, a teammate of Clemens' on Houston's 2005 World Series team.
It isn't clear how long Clemens will pitch for the Skeeters.
"This is a one game at a time thing," Hendricks said. "Let's see how he does on Saturday."
Some in baseball weren't quite as keen on the idea as Oswalt.
"He didn't travel with the Astros half the time toward the end there," Oakland pitcher Brett Anderson said. "I can't imagine him travelling for the Sugar Land Skeeters. I'm sure they'll draw a good crowd and it will be fun, but it's kind of those things you read about it and you're like: 'What's he doing?'"
Clemens is set to appear on the Hall of Fame ballot going to voters late this year. If he plays in another major league game, his Hall consideration would be pushed back five years.
Clemens was accused of using steroids and HGH in the Mitchell Report on drugs in baseball, something he denied. The Justice Department began an investigation concerning whether Clemens had lied under oath, and in 2010 a grand jury indicted him on two counts of perjury, three counts of making false statements and one count of obstructing Congress when he testified during a deposition and at a hearing that he never used any performance-enhancing drugs.
He was acquitted of all the charges on June 19 after a 10-week trial and has largely stayed out of the public spotlight until now.
"I think he's going to come back and try to prove a lot of doubters wrong," Oswalt said.
The signing was first reported by Houston television station KRIV.
AP Sports Writers Ronald Blum, Stephen Hawkins, Rick Gano and Janie McCauley contributed to this report.