Chaplin joined Coventry on loan from League One rivals Portsmouth in August
Goals from Jordan Shipley and Conor Chaplin saw Coventry City claim only their second league win of the season as they saw off struggling Oxford.
Jordan Shipley put City ahead with a shot from inside the box that deflected off U's defender John Mousinho.
Conor Chaplin then doubled the lead from the penalty spot with eight minutes to go after Shipley was brought down by U's keeper Jonathan Mitchell.
Jonathan Obika made it 2-1 late on when he headed in Luke Garbutt's corner.
Oxford boss Karl Robinson was forced to watch from the stands, as he served the second of a two-game touchline ban.
Coventry are now 12th in League One, four points off the top six, while the U's are second bottom having only won once this season.
Oxford manager Karl Robinson:
"Some of my players were not emotionally ready for this game. Emotionally, when things go against us, we're not very good.
"I was tearing my hair out because I was seeing players doing things we've never worked on. There are lots of little things we can do better.
"We always feel we can score but we've lost our momentum. And the league form is not acceptable."
Coventry boss Mark Robins:
"It was a really tight contest and I thought we just edged it.
"It's taken a hell of a lot of work to get ourselves two goals up. And we then conceded a rubbish goal from a set piece.
"But we held out under a bit of pressure at the end, without really looking in too much danger. We had to work really hard to get this second league win."
