The on-loan West Brom midfielder was making his first appearance since rupturing his anterior cruciate ligament while playing for Albion at Everton in late January.
Thorne was happy to be back in action after such a lengthy period on the sidelines but was frustrated by the defeat, which leaves the Hornets winless in five matches and down to 10th in the Championship table.
"I'm very pleased to be back playing. I had the injury and I was out for a while so I was a little bit more anxious before this game than usual, but I'm delighted to be back," Thorne told the club's official website.
"Ten months is a long time for anybody so I'm delighted to get through 90 minutes fine and I feel good. That's a positive for me to take away.
"I'm disappointed in the way we lost, though. We don't hide the fact that we should be pushing for promotion. Every game is one we need to be picking up points in, so we'll address things next week, go again on Saturday and try and get three points."