When looking at the possible No. 1 seeds for the NCAA Tournament three weeks ago, there were seven teams that had separated themselves from the rest of the pack. But after a string of upsets, that gap is narrowing as Selection Sunday approaches.

The importance of earning a No. 1 regional seed cannot be understated. Going back to 1982, No. 1 seeds in the NCAA Tournament have won the National Championship 19 times.

Teams such as The Associated Press‘ No. 4 Duke (26-3, 12-2 ACC), No. 7 Texas (24-6, 12-3 Big 12) and No. 9 San Diego State (28-2, 13-2 Mountain West) all lost last week, putting them out of the discussion for No. 1 seeds for now, said Jerry Palm, operator of CollegeRPI.com.

“It just seems like the whole top of the bracket is trying to play back to the pack,” Palm said. “They weren’t that far ahead to begin with.”

For the second time, No. 3 BYU (27-2, 13-1 Mountain West) took down San Diego State on the road Saturday, leapfrogging its conference rival in the standings.

The Cougars will earn a No. 1 seed to the Big Dance if they win the rest of their games, including the Mountain West Tournament, Palm said.

Because of the inherent hindrance of being labeled a “mid-major,” Palm said, BYU must win its conference tournament to earn a top seed — something teams from bigger conferences might not have to, including No. 1 Ohio State (28-2, 15-2 Big Ten).

“I think it depends on what other teams do. That’s the thing about seeding: It’s all relative,” Palm said of the importance of conference tournaments to teams vying for No. 1 seeds.

Because the Big East and Big Ten are arguably deeper than other conferences, the selection committee might be tolerant of OSU and No. 4 Pittsburgh (25-4, 13-3 Big East) not winning their conference tournaments.

In Palm’s bracket this week, his No. 1 seeds are OSU, Pittsburgh, No. 2 Kansas (27-2, 12-2 Big 12) and BYU. If the Buckeyes win the Big Ten Tournament, it’s likely they will take the NCAA Tournament’s top overall spot.

If Duke and Texas were to catch fire again and win their conference tournaments, it could put them in a favorable position in the eyes of the selection committee. Texas likely would replace Kansas, and Duke’s fate probably would rest on the performances of BYU and Pittsburgh in their conference tournaments.

The Buckeyes received 45 first-place votes in the AP poll this week, after being removed from the top spot for two weeks when the team lost two of three to No. 6 Purdue (25-5, 14-3 Big Ten) and No. 10 Wisconsin (22-6, 12-4 Big Ten).

Being the nation’s No. 1 team this late in the season gives OSU the driver’s seat for March Madness’ top overall seed, Palm said. Coach Thad Matta said he never paid attention to the rankings during the season, but he hoped his team’s body of work would speak for itself come Selection Sunday.

“I think it’s something that comes along with it. The one thing I’ve always said … we really want to be there in the end,” Matta said Sunday after his team dismantled Indiana (12-17, 3-13 Big Ten).

Senior guard Jon Diebler repeated the sentiment, noting that his team’s primary goal is to win the Big Ten Championship.

“That was our first goal when we worked out in the summer,” Diebler said. “Now we’re one game away from achieving that goal.”