Watson, who had been banned for violating the NFL's personal conduct policy for allegedly committing sexual assault, completed 12 of his 22 attempts for 131 yards with no touchdown passes and one interception.
The Browns' defense picked up Watson with two defensive touchdowns and a punt-return score to improve their record to 5-7, sitting third in the AFC North.
The three-time Pro Bowl quarterback had left the Texans for the Browns in the offseason on a five-year deal worth $230million guaranteed, one of the richest and most guaranteed contracts in NFL history.
That trade came after Watson had not played in the 2021 season as accusations emerged from more than two dozen women of sexual assault and other sexual misconduct during massage sessions, leading to the NFL-imposed 11-game ban and record $5m fine in August.
Watson's first NFL regular-season game in 700 days was met with displeasure, with his former fans booing and jeering him throughout.
"They're supposed to boo," Watson told reporters after the game. "I'm a Cleveland Brown now, and we're on the road, so they're supposed to boo."
Watson again refused to answer any non-football questions after the game, having been asked if he had any remorse for his actions that led to his suspension.
"That's something that, legal and clinical, we've answered before," Watson said. "They don't want me to address anything like that.
"Of course, it was a tough situation. The suspension was tough. But at the same time, my main focus is just trying to be 1-0 as a football player today.
"I was just excited to be back on the field today. I did everything that I was asked and was required to do. I did all that. I was able to play and be on the field today."
Browns head coach Kevin Stefanski conceded Watson was rusty after not played for a season-and-a-half.
"Obviously you're missing a bunch of time so you've got to get back in it," Stefanski said. "You've got to get this first one out of the way. But I know what the kid is capable of."
The Browns face the 8-4 Cincinnati Bengals next Sunday.