What time is it? Check out Serena Williams' $75,000 watch with 323 diamonds

Serena William's swag just reached new levels -- 'cause the tennis superstar got herself a new luxury watch that comes fully equipped with 323 DIAMONDS!!! 

It's called an Audemars Piguet Millenary timepiece -- made with 18-carat pink gold, a black mother-of-pearl dial and 323 brilliant-cut diamonds! The watch usually runs around $75K.

It certainly is a watch that only rich and affluent sportsmen can afford, Ghana Black Stars captain, Asamoah Gyan and NBA superstar Lebron James were both seen wearing ones recently.

A rep for Audemars -- popular with celebs like Jay-Z -- says the luxury watchmaker has a relationship with the tennis champ ... but this watch wasn't a freebie from them. 

"Serena is a friend of the brand but that isn't a piece we gave her," the rep tells TMZ Sports. 

So, did Serena drop $75k on gift for herself? It's not like she can't afford it.