They drew the Champions League round of 16 on Monday, and set up a mouthwatering match between Lionel Messi and Cristiano Ronaldo.

Then they drew it again, and that match was gone.

A “technical problem” meant that the Champions League was redrawn, leading to mostly new matchups — easier for some, harder for others — and shattering fans’ dreams of Paris St.-Germain vs. Manchester United.

After the initial draw, fans and teams began posting on social media hyping the matchups. But in the end, only one of those games will happen. Three hours later, officials reconvened to draw the teams again.

In the initial draw, Manchester United was matched with Villarreal. But those teams had met in the group stage, so a new name was pulled, giving Villarreal a match against Manchester City instead.

At that point, the ball with United’s name in it should have been put back in the bowl. That did not appear to happen, so United did not have a chance to be drawn against the next team, Atlético Madrid. The rest of the names were pulled, and the draw appeared to be concluded.

But as a result of the slip-up, UEFA, the European governing body, decided the fairest course was to pull all 16 teams again.

UEFA was happy to try to shift the blame for the goof, saying: “Following a technical problem with the software of an external service provider that instructs the officials as to which teams are eligible to play each other, a material error occurred in the draw for the UEFA Champions League round of 16.”

After the redraw, Chelsea wound up drawn against Lille, just as they had in the first draw. The other seven matchups were different however: Salzberg-Bayern, Sporting Lisbon-Manchester City, Benfica-Ajax, Atlético Madrid-Manchester United, Villarreal-Juventus, Inter Milan-Liverpool, and P.S.G.-Real Madrid.

The team that might be unhappiest with the new draw is Real Madrid, which started with a very winnable match against Benfica, and wound up playing the star-studded lineup of P.S.G. Still, Real leads the Spanish league comfortably and would seem to have every chance to come away with a win.

Pep Guardiola, the Manchester City manager, who started with a match against Villarreal and ended with one against Sporting, said: “It was a mistake. These things can happen, to managers, players and UEFA too. It is fair. It would be a mistake not to repeat, there would suspicions.”

Matchups in the second-tier Europa League tournament include Barcelona, making an unaccustomed appearance after finishing third in its Champions League group, against Napoli and Porto vs. Lazio.

In the new third-tier tournament, the Conference League, with a more eclectic mix of clubs, Leicester City will take on Randers of Denmark. Teams from Israel, Azerbaijan and Norway are also in the last 16.

Each of those tournaments was drawn just once. So far.