VAR made its UEFA Champions League debut this week at matches in Manchester, Rome, Amsterdam and at Wembley.

The technology was successfully deployed at all venues with the VAR teams embedded on-site at the different stadiums for the round of 16 first legs.

UEFA's chief refereeing officer, Roberto Rosetti, has worked with referees for several months in order to prepare them for the introduction of VAR in the world's most prestigious club competition. "I am very happy with the way VAR was implemented," he said. "The technology worked perfectly, and the refereeing teams performed at a very high level. It showed all the hard work we have put in." The first set of matches provided a number of incidents where VAR came into play.

Dušan Tadić was offside and then interfering with the goalkeeper ©UEFA.com

First VAR review

The first on-field review in a UEFA Champions League game took place at Ajax v Real Madrid, where a goal scored by the home side was ruled out following a VAR review.

Rosetti said: "As we communicated after the match on UEFA's social media platforms, the referee identified that the Ajax player was in an offside position and interfering with the goalkeeper, preventing him from playing or being able to play the ball, as the header was being made. This was in line with VAR protocol and the goal was correctly overturned and an indirect free-kick given for offside."

Goalkeeper Thibaut Courtois tangles with Tadić ©UEFA.com

Regarding the time it took for the review, Rosetti added: "The most important thing is that the referee took the right decision. Accuracy is more important than speed. Nevertheless we want to be as efficient as possible and we will try to improve this even more in the future. But we have to take into account that this was a very complex situation where VAR had to check two possible offside situations and the referee also had to consider the interference of the attacking player."

The handball incident occurred outside the area ©UEFA.com

In or out?

In the 19th minute of Roma v Porto, a potential handball by a Porto player occurred close to the penalty box, but the referee did not indicate an infringement.

Rosetti explained the situation as follows: "A subsequent check by VAR showed that the incident was outside the penalty area, and therefore VAR did not intervene and play continued correctly. This was in line with the IFAB VAR protocol which only allows VAR to intervene in the four match-changing situations."

A close-up of the handball incident at Roma v Porto ©UEFA.com

There was another check for potential offside for Porto's goal in the 79th minute, where VAR confirmed there was no offside and the goal stood.

Something to flag up?

During Manchester United v Paris Saint-Germain there was no significant VAR intervention, but there was a situation where the assistant referee delayed raising his flag.

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Rosetti said: "In this case, the assistant referee correctly delayed raising his flag against a Paris player as this was a tight offside and a clear goalscoring opportunity. Again, this was in line with VAR protocol, which encourages assistant referees to delay flagging for tight offsides when a player is about to score, since decisions can be reviewed in the event of a goal being scored."

VAR is being used in the UEFA Champions League from this season's knockout phase onwards, and will also be deployed at the UEFA Europa League final, UEFA Super Cup, UEFA Nations League Finals as well as the UEFA European Under-21 Championship.