The former #1 player in the world said, 'Yes' to NBA star David Lee ... 8 months after going public with their relationship.

"Happiest day of my life yesterday saying yes to my soulmate," Wozniacki said ... while posting a photo of her MASSIVE engagement ring.

FYI, Lee has reportedly made more than $92 MILLION during his NBA career -- so ... not bad!

Wozniacki was previously engaged to golfer Rory McIlroy -- but things ended terribly in 2014 when he called things off AFTER they sent out the wedding invitations.

They've both moved on ... and Lee seems like he's in for the long haul.

Congrats!