Credit: Craig Barritt/Getty Images; Jason Merritt/Getty Images

Alex Pettyfer's scary tantrums got him banned from a pre-Oscar party on Feb. 26, but his ex-girlfriend Dianna Agron was free to party -- and flirt! -- the night away.

An insider tells that the single-again Glee actress, 24, hit the Weinstein/Montblanc pre-Oscar bash at L.A.'s Soho House with close pal Jessica Szohr (Gossip Girl).

Around 1:00 a.m., Agron got into a long, intense chat with Chris Evans. "They were definitely flirting," the witness tells Us of Agron and the hunky Captain America star, 29.

(Also flirting with Agron and Szohr, with less success, according to the party witness: Gerard Butler and Dane Cook.)

About a half an hour into the heart-to-heart, "Chris grabbed Dianna's hand and kissed her knuckles," the reveler says. "It was sweet!"

When Agron and Szohr were ready to leave, Evans went "in for a close cheek kiss and hug with Dianna."

Is Agron ready to love again after her ugly breakup from Pettyfer, 20? "It seemed like Chris was more smitten than Dianna," the source says.