Kylie Jenner showed up to support her man, Timothée Chalamet at the Oscars Sunday -- locking lips with the star as he aims to become the youngest best actor winner in history.

The reality star pulled up to Hollywood's biggest night in a low-cut black dress ... cut out in the middle to reveal some of her taut tummy.

She talked quietly with Timmy who looked like a ray of sunshine in his all-yellow suit ... and, the two leaned in to lock lips during the classy affair.

Kylie's been spotted at a number of big award shows with Chalamet during this season ... hanging out with him at the Berlin Film Festival and sharing a big kiss during the Golden Globes.

Of course, Chalamet's up for Best Actor for his portrayal of Bob Dylan in the flick "A Complete Unknown." If he wins, he will become the youngest actor to ever win the trophy -- beating out Adrien Brody's win for "The Pianist" who was just a few days shy of 30.

BTW ... Kylie's appearance out is the first since her pal and hairstylist Jesus Guerrero unexpectedly passed away last weekend.

Jenner admitted the loss is still hitting her hard ... making it difficult for her to sleep. She's covering all the funeral expenses for Jesus as well.

Worth noting ... Kylie and Timothée didn't walk the red carpet together -- but a whole lot of other people did, and we've got all their pictures ready for you to peruse.

Looks like Kylie's enjoying quality time with her man ... and, she's almost certainly keeping her fingers crossed that he takes the golden statue.