For many young pro athletes, their first paycheck from the big leagues is the most money they've ever seen. In some cases, it can make them millionaires overnight. Here's how six star athletes celebrated first big paycheck.

Shaquille O'Neal blew through $1 million in 60 minutes

Within an hour of signing his first professional contract in 1992, Shaquille O'Neal had already gone on a shopping spree and was down over $1 million. The NBA star's first purchase was a $150,000 Mercedes Benz. He immediately followed that up with a matching one for his dad and a smaller $100,000 one for his mom. The rest of the money went towards paying off his mom's house and doing "what all the homeboys do — gotta buy rings and diamonds and earrings and this and that," he told Business Insider. O'Neal, who played for 19 seasons before retiring in 2011, later learned how to keep his spending in check. But looking back on that day, he says, "it was well worth it."

Venus Williams went straight to the bank

Tennis legend Venus Williams started earning big money from a young age: When she won her first Grand Slam title at age 20, it came with a check for £430,000. But rather than splurging, Williams saved every penny. "I really didn't spend any of it," she tells CNBC Make It. "I just didn't want to become a statistic, or one of those athletes that had it all and then in the end had nothing. That was always in the back of my mind, so it made me want to be more realistic with how I spent money."

Harrison Barnes bought his dream mattress

Harrison Barnes #40 of the Dallas Mavericks Streeter Lecka | Getty Images

"The first thing I bought was a really nice bed," Harrison Barnes of the Dallas Mavericks tells CNBC Make It. "For me, growing up, really having a nice bed was something that I always wanted." Barnes, who was drafted 7th overall in 2012 and earned a $2.8 million salary as a rookie, did his research before making the purchase: "I definitely tried out every bed in the mattress store." It was "like Christmas," he added. "You have the ability and are fortunate enough to be able to choose whatever you want, which was new for me. Usually, whatever store I walked in, I'm buying the cheapest thing possible, if that. So to be able to go into a mattress store and say, 'I'm going to choose the bed I want to sleep on,' and choose one of the nicer ones, that was pretty cool."

Andre Iguodala headed to Niketown

Andre Iguodala #9 of the Golden State Warriors Andrew D. Bernstein | NBAE | Getty Images

Andre Iguodala's first NBA contract was "for four years, $9 million," he tells online investing service Wealthsimple. "You get an advance over the summer and, just before the draft, you get an advance for trading cards and an advance for a shoe contract. I remember a loan agency floating me until I got the advances. They sent me a check for $25,000." The Golden State Warriors star, who was 20 at the time, bought "a whole bunch of pairs of Jordans," he says. "I spent like two or three grand and it felt like I spent a million dollars. I didn't know how to spend money."

Ryan Broyles paid off credit card debt

Wide receiver Ryan Broyles speaks during an event to educate teens about financial responsibility Tom Williams | Getty Images

When Ryan Broyles entered the NFL draft, his credit report "was terrible," he writes on The Players' Tribune. "I had late payments. Delinquent bills. Accounts in collections. It was bad." So after signing a $3.6 million rookie contract with the Lions, the first thing he decided to do was pay off his debt and set up automatic payments for his bills. Since then, Broyles has chosen to live on a modest $60,000 a year and stash the rest of his NFL salary in investments and retirement savings accounts.

Daniel Norris bought a $14 T-shirt