It was Argyle's second successive victory, with on-loan Sheffield Wednesday striker Caolan Lavery the catalyst.
Lavery's first-time drive from the edge of the box, after a goalless first half, put the Pilgrims on the front foot.
Sheridan said: "I thought the second half was very exciting to watch.
"To score three goals against a team that is flying at the moment can only give us confidence.
"Obviously the forwards Reuben and Caolan will take the plaudits for the goals, but it was a really excellent team performance."
"The result wasn't a shock to me because I know how well we have been playing," Sheridan added.
"I thought we played really well and thoroughly deserved it.
"We were very lively on the counter. The only disappointment to me was that we gave the ball away a bit too cheaply in their half of the pitch.
"But it's good to beat one of the best teams in the league and it will give us a lift.
"I think we should be higher up in the league than we are, and now we are getting a bit of consistency and a bit of belief.
"They (Oxford) were putting balls in the box late on, but I thought we defended very well against some good players."
- Sports & Recreation
- Reuben Reid
- Caolan Lavery
- Dave Kitson