Chamberlain struck out the side after allowing a leadoff single in the eighth, sitting down the final of six batters he faced looking at a sharp curveball. He threw 30 pitches over 1 1/3 innings, 23 for strikes, with three strikeouts and no walks.
"The physical part is over, now it's the mental part -- that's the hardest thing," Chamberlain said. "Knowing I can throw everything with conviction was the least of my concerns. Now it's getting in the pace of the game, getting in the flow, and getting an idea of what you want to do pitch to pitch."
Chamberlain threw a fastball that hovered between 94 and 98 mph, a curveball that got two strikeouts looking, and a slider and changeup.
He said there is no lingering discomfort from an open dislocation of his right ankle suffered in the spring, or the Tommy John surgery he underwent last June, and he has already pitched on back-to-back days.
Chamberlain wanted to enter the seventh with runners on base -- a situation he has yet to face in six rehab appearances with the GCL Yankees and Class A Advanced Tampa -- but he at least faced tougher at-bats against the Washington Nationals' Double-A affiliate.
Harrisburg first baseman Tim Pahuta worked a nine-pitch at-bat against Chamberlain in the eighth, fouling off three pitches before missing on a slider.
"It's great to see those at-bats," Chamberlain said. "The two outings before, I threw nine pitches and 10 pitches. To be able to get into some extended at-bats and get some guys who have been around a while, have seen some guys and know that they have a plan at that plate, that's the biggest obstacle."
Chamberlain will return to Yankee Stadium on Monday to play catch, but he is unsure of when he will return to the active roster. His rehab assignment began July 10, and he must return to the big leagues after 30 days, barring any setbacks. Manager Joe Girardi said Chamberlain will likely require at least another rehab appearance, and Chamberlain estimated it could be Tuesday.
The 26-year-old made the most of his time in Trenton, where he made eight appearances in 2007 as he worked his way through the Yankees' system. He signed autographs for about 40 minutes before the game at Waterfront Park, and remained in the dugout to watch a Thunder rally after finishing his outing. He turned to the crowd and pumped both fists in the air as Trenton turned a 2-0 deficit into a 3-2 advantage in the bottom of the eighth, giving Chamberlain the victory.
"Being around these kids and the grind they go through, being able to take a step back -- once you're in the grind of year after year, you can't get out of your own way," said Chamberlain, who last pitched in a big league game on June 5, 2011. "I thought there should have been a time where I stepped back and looked at things and taken appreciation.
"Things go so fast sometimes that you can't do that. To be able now to have some time and realize how fun this game is, and to make my stops again and know how fortunate I am to play this game and put this uniform on every day is something I can't forget."
Steven Miller is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.