A 20th NBA Slam Dunk champion will be crowned this weekend in Denver. Fans will watch some of the world's greatest athletes perform in a competition rooted in the sheer athleticism of the game. But how did the dunk contest start, and what was the first contest like? Now you can watch for yourself.

In 1976, the ABA held the first Slam Dunk Contest at halftime of their All-Star Game in Denver. That contest featured a battle between two of the top dunkers of all-time -- David Thompson and Julius Erving. Thompson was an explosive rookie with the Denver Nuggets, and, naturally, the hometown favorite. Erving was the veteran leaper from the New York Nets and the ABA's career scoring leader. George Gervin, Artis Gilmore and Larry Kenon rounded out the field. Decked out in wild hair-dos and the form-fitting uniforms of the era, the players tried to out-do each other with a wide selection of jams, dunks and slams.

1976: ABA Dunk Contest

Dr. J Foul Line Dunk: 300k
Thompson Double-Pump: 300k Full Dunk Contest: 300k
Sadly, it's safe to say that not a lot of people saw this original dunkathon. The sellout crowd in McNichols Arena, and the TV audiences in the ABA cities of Denver, Indianapolis, Louisville, San Antonio and St. Louis were the only ones to see it live. Thankfully, you can watch the whole contest here: 300k .

The rules gave each dunker two minutes to do five dunks. Two dunks were mandatory: standing under the basket, and taking off 10 feet from the basket. The other three dunks had to be one from the right side, one from the left side, and one from either of the baseline corners.

In order to protect the baskets, the dunkers had to alternate sides so as not to put too much stress on the rims. There were no rounds to advance to; each player did his five dunks and that was it. The judges rated the dunkers on artistic ability, imagination, body flow and fan response. The dunks weren't scored individually, and the results were held until the end.

By a random draw, Gilmore, Kenon and Gervin went first. Then Thompson went, followed by Erving.

Thompson thoroughly impressed the crowd, getting the best fan response out of any the dunkers. In the end, he may have hurt his chances by missing one of his dunks. But his double-pump reverse (you can watch it here: 300k) and 360 from the baseline would have stood up in any dunk contest.

Any dunk contest that didn't include Dr. J.

Erving took the court and wasted no time making his mark. On his second dunk, rather than jumping from the mandated 10-foot line, he launched himself from the 15-foot foul line (you can watch it here: 300k). This became one of the most memorable dunks in basketball history, and was later used by Michael Jordan and others in later dunk contests.

Erving followed the free-throw line dunk with a reverse from the right, then a swooping hang-on-the-rim dunk from the left. He then finished with a baseline scissor move that was just as impressive as the rest.

Ultimately, Erving was declared the winner without a big media session or a trophy. After the low-key announcement, the players went on and played the second half of the game.

The next dunk contest wasn't until 1984, with the NBA All-Star Game in Denver. So it's plain to see just how much high-flying history there is to be found in the Mile High City.