The Boston Celtics and Golden State Warriors enter this year's NBA playoffs in a good position, as both squads earned their respective conference's No. 1 seed.

However, simply being the No. 1 seed doesn't guarantee that a team will advance to the second round. In fact, five No. 8 seeds have pulled off first-round upsets over the course of NBA history.

Since 2007, three No. 8 seeds have accomplished the impressive feat - the 2007 Warriors, 2011 Grizzlies and 2012 76ers.

The Chicago Bulls and Portland Trail Blazers will try to add their names to that list starting this weekend, but will have to do so in two of the toughest road environments in the entire NBA.

Of the five times a No. 8 seed has taken down a No. 1, some were flat-out surprising, while others had plenty of warning signs. Here's a ranking of the most surprising No. 8 seed upsets of all-time:

2011: No. 8 Memphis Grizzlies over No. 1 San Antonio Spurs (4-2)

Under coach Gregg Popovich, the Spurs have been one of the best franchises in the entire league. They have a signature brand of mistake-free basketball, which has led to five titles since 1999.

The Spurs hardly ever make early playoff exits, but that wasn't the case in 2011, when the Memphis Grizzlies' stifling defense helped them take down San Antonio in six games.

Though the Grizzlies fell to the Oklahoma City Thunder in seven games in the second round, they are one of the few teams that can say they forced a Popovich-coached team to make an early playoff departure.

2012: No. 8 Philadelphia 76ers over No. 1 Chicago Bulls (4-2)

It's almost comical (in a sad way) how much misfortune the Bulls had to deal with in the 2012 playoffs.

First, after earning the No. 1 seed in a lockout-shortened season, star point guard Derrick Rose tore his ACL in Game 1 of the series. The Bulls then lost center Joakim Noah to injury as well, erasing any hope Chicago fans had of advancing.

The fact that the Sixers won Game 6 79-78 on late free throws from Andre Iguodala should tell you all you need to know about how ugly the series was.

1994: No. 8 Denver Nuggets over No. 1 Seattle SuperSonics (3-2)

The Nuggets were the first No. 8 seed to pull off an upset over a No. 1 seed, taking down Gary Payton, Shawn Kemp and the SuperSonics in five games.

Dikembe Mutombo, LaPhonso Ellis and company would go on to lose to the Utah Jazz in the next round, but before they made their playoff exit, they provided fans with something no one had ever seen before.

2007: No. 8 Golden State Warriors over No. 1 Dallas Mavericks (4-2)

This upset was definitely exciting, but it wasn't exactly a huge surprise. There were signs the Warriors were peaking at the right time heading into the first-round series.

The Warriors won all three games against the Mavericks during the regular season and averaged 106.5 points per contest. Baron Davis, Stephen Jackson and coach Don Nelson's crew wanted to make the series a shootout, and they succeeded, winning in six games.

The Warriors went on to lose to the Utah Jazz in the second round in five games.

1999: No. 8 New York Knicks over No. 1 Miami Heat (3-2)

A lockout shortened the 1999 season to only 50 games, so the gap between the Heat and Knicks entering the playoffs may have been a bit deceiving.

Who knows what would have happened over 82 games, but the No. 8 Knicks cruised in the playoffs, making it all the way to the NBA Finals before falling to the San Antonio Spurs.