updated 07/19/2010 AT 2:00 PM ET
•originally published 07/19/2010 AT 3:50 PM ET
Arriving separately at his teammate CC Sabathia’s 30th birthday bash at New York’s 40/40 Club, the couple strategically steered clear of one other and any prying eyes. In fact, Diaz, 37, slipped in and out through the side door while the Yankees slugger, 34, used the front entrance.
“It was obvious that they were deliberately avoiding each other,” a source tells PEOPLE. “The two of them seemed hyper-aware that everybody was staring at them, waiting for them to interact.”