The first two rounds of the NCAA Tournament are complete, and the contenders are beginning to separate themselves from the rest of the pack. While the number of upsets in the early rounds was underwhelming, it set up some titanic tussles in the Sweet 16. Purdue-Gonzaga, Houston-Duke, and North Carolina-Alabama are among the fascinating contests on display in the coming days.

Which game is the best? Find out in our ranking of the eight Sweet 16 matchups.

1) #1 Purdue vs. #5 Gonzaga

As the only Sweet Sixteen that is the rematch of a regular season game, the Purdue-Gonzaga contest has an added layer of intrigue. The Boilermakers beat the Zags by 10 points in the first round of the Maui Invitational back in November, coming back from a nine-point first-half deficit to pull away late.

Both coaches insist this is a new matchup between two completely different teams. Gonzaga shot just 6-32 from deep in that game but is 42.6% from beyond the arc in its last 12 games, including 50% in the NCAA Tournament. Graham Ike has also established himself as a scoring force down low while Ben Gregg's insertion into the starting lineup sparked a struggling Gonzaga team. Expect a March Madness classic in this barn burner of a matchup as Zach Edey looks to win a national championship in what is likely his final collegiate season.

2) #2 Tennessee vs. #3 Creighton

Two of the best wings in college basketball face off in this one as Tennessee's Dalton Knecht goes up against Creighton's Baylor Scheierman. But other than high-scoring small forwards, these are two very different teams. Creighton throws up threes often and with considerable effect (eighth in three-point rate, and 33rd in accuracy) while Tennesse relies on its defense to get things done. The Vols allowed opponents to take a high number of threes but are effective at forcing bad attempts (309th in three-point rate allowed by 29th in 3P percentage).

Despite recent success, both teams are still desperately looking to break through to the Final Four — adding another layer of intrigue to what should already be an exciting contest.

3) #1 Houston vs. #4 Duke

A game with numerous NBA talents on both ends of the floor, the expected slow tempo puts this one lower. Duke ranks 245th in adjusted tempo while Houston is near the bottom of Division I at 345th. Houston's swarming defense will look to turn this one into even more of a slog, and its offense — while effective — is often ugly to watch with one of the highest mid-range attempt rates in the country.

With future NBA first-round picks Kyle Filipkowski and Jared McCain, Duke has the best shot of any team in the South Region to knock off Houston. The result is a close but possibly messy game.

4) #2 Iowa State vs. #3 Illinois

The nation's number one offense against the number one defense. Illinois is scoring 126.8 points per 100 possessions while Iowa State is giving up nearly 40 points fewer per 100 possessions. Their weaknesses on the other side of the ball made them upset candidates, but each survived a close game to reach the Sweet 16. The offense-defense dichotomy on display makes for a fascinating game between these two Midwestern programs.

5) #1 North Carolina vs. #4 Alabama

Which Alabama team will show up in this game? Against Charleston, the Rolling Tide racked up a tournament-high 109 points. Two days later, Alabama combined with Grand Canyon to produce 27 turnovers while shooting from 10-51 from three-point range. Both teams rank in the top 45 in the country in tempo and the top 15 in adjusted offensive efficiency, though Bama's poor defense and recent volatility mean an increased chance of a blowout.

6) #2 Arizona vs. #6 Clemson

Clemson rose as high as 13th in the AP Poll this season before falling out of the top 25 in January. The Tigers are looking like a top-15 team again after convincing wins over New Mexico and Baylor, and they have done so despite All-ACC First Team big man PJ Hall playing fewer than 20 minutes in each contest due to foul trouble.

Arizona won its two opening games in slightly unconvincing fashion, combining a strong half of play with a mediocre half en route to the expected margin of victory. This will be a good contest, just not as exciting as the other Sweet 16 matchups.

7) #1 UConn vs. #5 San Diego State

A rematch of last year's National Championship Game, this contest is shaping up to be a UConn route like last year. SDSU squeaked by UAB then defeated a Yale team that was overmatched physically. Meanwhile, UConn routed Stetson and did not trail by fewer than 16 points in the second half against Northwestern. Few teams are playing better than the Huskies right now and San Diego State does not have the scorers to match the Big East champs.

8) #2 Marquette vs. #11 NC State

Despite being the only remaining double-digit seed, NC State is not the biggest underdog in the Sweet 16. That honor belongs to San Diego State — an 11.5-point underdog compared to NC State as a 6.5-point dog. The contrast in styles — NC State's slower, halfcourt pace versus Marquette's havoc defense and tendency to push in transition — will be interesting. But it is hard to see NC State keeping up with Marquette's high-flying offense in the Sweet 16.