When the NCAA Tournament reaches the Sweet 16, that means there are only 15 games left to decide a national champion.

Kentucky needs to win four of those games to become the first undefeated champion since Indiana in 1976. The Wildcats improved to 36-0 - the best start to a season for any team - with a workmanlike win over Cincinnati. Next up in the Midwest Regional semifinal is West Virginia, another team that will come right at Kentucky and try to force turnovers, the Mountaineers' trademark this season.

The East Region changed dramatically entering the Sweet 16 with top seeds Villanova and Virginia ousted. It's the first time since 2004 - and eighth time ever - that the top two teams from one region failed to advance to the second week.

The Atlantic Coast Conference and Pac-12 entered the round of 32 as the only leagues with three or more teams not to lose a game. The ACC is 11-1 with Virginia's loss to Michigan State the only blemish. The Pac-12 is 7-1 following Oregon's loss to top-seeded Wisconsin.

Here are some story lines to watch as the Sweet 16 approaches:

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REMATCH REPLAYS: Two of the eight games in the regional semifinals will be rematches from the regular season.

UCLA and Gonzaga met on Dec. 13 in Los Angeles, and the then-No. 9 Zags came away with an 87-74 victory. Kyle Wiltjer scored 24 points and Byron Wesley added 20 points for Gonzaga.

Bryce Alford scored 23 points and Isaac Hamilton added 18 for UCLA.

Louisville and North Carolina State met in an ACC game on Feb. 14 and the visiting Wolfpack prevailed 74-65. Cat Barber had 21 points for N.C. State, which held Louisville to 33 percent shooting and outscored the Cardinals 32-16 in the paint.

"We got dominated at all five positions tonight," Louisville coach Rick Pitino said then.

Chris Jones, who was dismissed from the program last month, scored 20 points and Wayne Blackshear added 19 for then-No. 9 Louisville. Terry Rozier and Montrezl Harrell, Louisville's leading scorers, combined for 14 points.

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SWEET SEEDS: The West Regional will be the toughest of the four in the Sweet 16 if you believe the seeds.

Top-seeded Wisconsin will play No. 4 North Carolina and second-seeded Arizona will face No. 6 Xavier in Los Angeles, a total of 13 when the seedings are added.

The Midwest is second with 16 (No. 1 Kentucky vs. No. 5 West Virginia and No. 3 Notre Dame vs. No. 7 Wichita State), while the South is next with 19 (No. 1 Duke vs. No. 5 Utah and No. 2 Gonzaga vs. No. 11 UCLA).

The last of the regionals is the East where third-seeded Oklahoma meets No. 7 Michigan State and No. 4 Louisville faces eighth-seeded North Carolina State, a total of 22.

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