Amar’e Stoudemire participated in his first scrimmage yesterday — a 3-on-3 at the Knicks’ Tarrytown practice facility and was outplayed by third-string center Earl Barron. Stoudemire is still shooting to make his return Saturday in Game 3, but looked winded, out of rhythm and plain rusty. Barron blocked a couple of his inside shots. Stoudemire blew a dunk, and Barron and Chris Copeland each scored over him in the post, with Stoudemire occasionally losing his balance and winding up on his rump. Mike Woodson and the entire coaching staff watched the scrimmage in silence. “It feels good to finally be on the court [in] competition,’’ Stoudemire said. “I had tough day today but it felt really good.’’ The lackluster scrimmage hardly dampened Stoudemire’s confidence. Asked the adjustment from going to his heavy running and drills to a contact scrimmage, Stoudemire said, “It’s natural. Playing basketball is a natural ability. I was born with it. It’s not going to go anywhere. It’s like riding a bike. Once you learn, it never goes away. It’s a matter of getting back in top shape, sharpening up on certain skills and getting crisp. It takes time.’’ Stoudemire hasn’t played since March 7 after undergoing his second knee debridement surgery of the season. He played alongside Marcus Camby and James White in the blue jerseys while facing the white-shirted trio of Barron, Copeland and Quentin Richardson. When it ended, he lay on the floor on his back in exhaustion. “I had no pain running, cutting, slashing — I felt explosive,’’ Stoudemire said. “The one thing is getting my wind back up and go from there. The recovery is going well. I’ve been doing everything I can do to get back into top form.’’ Stoudemire will rest today and hopes to scrimmage tomorrow, Thursday and maybe Friday. The Knicks have three days off between Games 2 and 3.