Tennis Legend Ivan Lendl Lists CT Mega-Mansion, $16.4 Million Price Tag!!

Tennis legend Ivan Lendl -- the former #1 ranked player in the world and 8x Majors winner -- is unloading his INSANE Connecticut mansion ... and the 445 acres of land it sits on!!

TMZ Sports has learned the 61-year-old retired Czech-American tennis star listed the Cornwall, CT estate -- about a 2-hour drive from New York City and Boston -- and it's absolutely breathtaking.

Asking price ... $16.45 mil!!

The 18,000 square-foot mansion boasts 10 bedrooms, 15 bathrooms and comes with every ridiculously lavish amenity you could ever want in a home.

We're talking a full gymnasium, workout room, 2 locker rooms, sauna, granite outdoor pool, fishing pond, barn with horse paddocks ... and of course, a tennis court!!

If you're not familiar with Lendl -- who retired in 1994 -- he's one of the greatest tennis players of all-time. In fact, he was ranked the #1 player in the world for 270 weeks.

IL racked up 144 career tourney wins ... including 8 Grand Slam singles titles. He won the US Open and French Open each 3 times and the Australian Open twice.

You're probably asking ... how'd he afford this gorgeous house?!

Well, the Tennis Hall of Famer reportedly made $21 mil from prize money alone (he's also been super successful off the court).