The Maroon 5 frontman took on presenting duties for Saturday's programme and opened the show by discussing his TV job as a mentor on America's The Voice.
He told viewers, "I've been a coach on The Voice for the past two years so tonight, I just hope you don't judge me too harshly."
Funnyman Andy Sandberg immediately spun around in a big red chair, similar to those used by Levine and his fellow mentors on the singing competition, and quipped, "Fat chance Levine", before trying to encourage the star to join his team.
Diaz then made a surprise appearance as a rival judge and referenced her famous mohawk hairstyle in 1998 film There's Something About Mary as she attempted to land Levine as her comedy protege.
She told him, "If you want to succeed in comedy, you have to check your pride at the door. You have to be willing to fall down, you have to be willing to shake your butt, you have to be willing to take a handful of Ben Stiller's spooch (sic) and put it right in your hair and spike it up like a mohawk!"
She went one step further by urging him to strip off, adding: "Adam, I've hosted before, so trust me, the first thing you should do as a host, is take your shirt off. Just take it off... Lose the shirt."
Jerry Seinfeld, another unexpected guest in the opening segment, appeared as a third The Voice coach and objected to Levine taking his clothes off - but his words of wisdom fell on deaf ears as Levine had already peeled off his top to show off his tattooed chest by the time the camera panned back to the singer.
Other sketches on the show featured Levine challenging impersonators of veteran pop band Train to a dance off, while he also helped Samberg and his Lonely Island rap trio make a comeback with their latest digital short, Y.O.L.O. (You Oughta Look Out), a play on the popular You Only Live Once phrase.
The promo for the cautionary comedy tale also featured Saturday Night Live's musical guest, rapper Kendrick Lamar, dressed as a geeky financial consultant.