In a span of four days, college basketball fans were treated to the best and worst of Duke. In fact, the same could be said about the 40 minutes of action at Louisville on Saturday.

On Wednesday, the Blue Devils rallied from an eight-point deficit to beat rival North Carolina despite being even more shorthanded than usual after Matt Jones sprained his ankle. It was their fifth straight win and third straight against a high-profile opponent, joining home wins over Louisville and Virginia. They again showed signs of just how talented they are and how capable they are of winning against anyone on any given night.

On Saturday, No. 20 Duke made its return trip to No. 18 Louisville and showed just how fragile it is in a 71-64 loss to the Cardinals that featured a late-game meltdown. This was the Duke that should terrify anybody who picks the Blue Devils to advance far in the NCAA Tournament bracket.

Duke led 52-41 with 11:38 left, which means Louisville out-scored the Blue Devils 30-12 the rest of the game. Just about everything that could go wrong did go wrong for Duke down the stretch, including going about half of the second half without making a jump shot.

Despite participating in warm-ups, Jones did not actually play for Duke, meaning two Blue Devils starters were on the bench, as forward Amile Jefferson has been out since December. Without Jones and Jefferson, Mike Krzyzewski has only five players he really trusts, and he was forced to play freshman forward Chase Jeter by necessity. Jeter entered the game averaging seven minutes and 1.5 points per game, and on Saturday he played 17 minutes and finished with five points and two rebounds.

Things got even more precarious for Duke because of foul trouble and another injury scare. Freshman guard Derryck Thornton briefly left the game in the second half after injuring his shoulder. He returned and played 34 minutes, scoring seven points. Duke was lucky that he was able to return, because both star Grayson Allen, who scored 29 points, and freshman Luke Kennard fouled out.

A minute after Krzyzewski was assed a technical for arguing an offensive foul on Allen, Allen was called for another offensive foul with just under four minutes left, sending him to the bench with five. He was then also hit with a technical for arguing on his way out. Kennard fouled out with 21 seconds left, forcing walk-on guard Nick Paglicua into the game briefly.

By then, it was too late. Duke had already blown the lead.

After the game, Krzyzewski said that he expects Jones to return to action when Duke hosts Florida State on Thursday and that Thornton's injury wasn't serious. With the Seminoles, Pitt and Wake Forest the next three games before the regular season wraps up with North Carolina, Duke has a chance to regroup and get back on track after a brutal run of tough games that was largely successful.

It's not that losing at Louisville is inexcusable or surprising in any way. Despite the Cardinals' banishment from the NCAA Tournament, they're still a talented team that has the nation's No. 1 defense, according to Ken Pomeroy's ratings. Duke should be thrilled going 3-1 during this stretch of four games in a row against ranked teams.

What's troublesome for Duke is how quickly things can go bad because of the thin margin for error the roster has as currently constructed. In the first half, Duke built an eight-point lead behind the outstanding play of Allen, who had 19 points in the first 20 minutes. He had an eventful day, getting elbowed in the face at one point and then fouling out later as Duke let its lead slip away. Allen was Duke's only player to score in double figures, as Ingram struggled, finishing with eight points and 10 turnovers.

If either Ingram or Allen is not playing well, Duke doesn't have other consistent options. On Saturday, it was stuck with four players playing at least 34 minutes, three of whom are freshmen, against a great defensive team, and it clearly ran out of gas late in the game as the lead slipped away.

Wednesday showed that Duke can win any individual game (North Carolina proceeded to respond to the loss by torching Miami on Saturday). But Saturday's trip to Louisville showed how quickly things can go wrong for Duke, which, despite its recent run of success, is still a talented but thin team prone to defensive lapses and especially vulnerable when injuries and/or foul trouble strike. The Blue Devils have upside, but unless Jefferson returns and they stay healthy, that's not a recipe for success in tournament play.

It managed to do so at North Carolina, but Duke isn't built to survive bad luck.