The two were acting like more than friends at Friday's SHG's Eden Hollywood opening and were "constantly touching and kissing each other," a witness told People magazine.
After arriving with friend Brittany Snow around midnight, the pair quickly took to the dance floor. "Vanessa was bopping around with her arms up while Zac had his hands all over her," the source said. "Vanessa had a smile on from ear to ear, and the two were inseparable after that."
At a table, the couple got cozy, and stayed that way for the rest of the night.
"Zac sat in between her legs and she wrapped her arms around him," the onlooker said. "They were making out on and off for the last hour or so until closing. They acted like there was no one else in the room."