Dustin Richardson had only performed in front of a larger television audience once before — and that was as a basketball player.

Richardson, a fifth-round pick in the 2006 draft, made his major league debut Monday night, pitching 1-1/3 scoreless innings out of the Red Sox bullpen after previously spending the ’09 season between Double-A Portland and Triple-A Pawtucket. And while it was undoubtedly the largest crowd the 6-foot-5 lefty has ever performed in front of, he had showcased his skills before a larger TV viewership three years prior.

Richardson was one of the two finalists on the ESPN reality show “Knight School,” in which students from Texas Tech University competed for a chance to make Bobby Knight’s men’s basketball team as a walk-on.

“That whole ‘Knight School’ thing was so long ago, it seems,” Richardson said.

But with two outs in the fifth inning, those reality show memories got pushed back even further as Richardson was called upon to face Toronto’s Aaron Hill. One pitch and one fly ball to center field, and the 25-year-old officially was a big league pitcher.

“[Monday night] I was numb. It happened so fast. It was a blur,” said Richardson. “It took until about the third inning, while sitting in the bullpen, that I started feeling like a baseball player again. I had been here before with the Futures at Fenway earlier this year, but obviously it’s not quite the same. The fans, at night … I don’t want to say it was scary, but I kind of just wanted to hit the fast-forward button to get through it all.”

Richardson, who wore No. 54, went a combined 2-2 with four saves and a 2.55 ERA over 45 relief appearances between Portland and Pawtucket. He compiled a 2.70 ERA in 38 games with Portland, earning Eastern League All-Star honors and holding opponents to a Double-A-best .186 average. Richardson had been promoted to Pawtucekt on Aug. 21, giving up two earned runs over 10-2/3 innings with 16 strikeouts in his final seven appearances.

All of the cachet that came with his success was put on the back-burner, however, as the sudden “oohs” and “aahs” emanating from the stands reminded Richardson.

“The roar of the crowd was incredible,” he said. “I’m sitting in the bullpen and a lot of offense was going on and I’m just hoping that didn’t happen to me.”

Richardson had been working out for the past 1-1/2 weeks in Fort Myers with a collection of other Red Sox minor leaguers who provide the kind of insurance the pitcher supplied Monday.

“I didn’t find out until 1 o’clock,” he said. “I almost threw this morning. I was getting ready to warm up, but they shut me down because something was going on and they told me to sit tight.”