The 20-year-old actress and 52-year-old star stunned in high-slit dresses while attending the movie's Los Angeles premiere at the TCL Chinese Theatre with Tom Holland.
"Over the moon right now...goodnight, sweet sweet dreams," she tweeted to her 7.9 million followers after the event.
Tomei, meanwhile, wore a Zuhair Murad dress with sheer lace panels. She told Entertainment Tonight the dress channeled her character, Peter Parker's aunt May, whom she previously said will be "sexy" in the film.
"I didn't really know what Aunt May looked like until after I signed on," the actress told reporters at a news conference Sunday.
"[The filmmakers] kept going, 'She's going to be sexy,'" she recalled. "These guys had the vision of how it was going to be revamped and everyone was going to be younger and she is his aunt by marriage, so she could really be any age."
Spider-Man: Homecoming stars Holland as Peter Parker, aka Spider-Man, with Zendaya as Peter's classmate Michelle and Keaton as Adrian Toomes, aka Vulture. The movie opens in theaters July 7.