MOSCOW • The video assistant referees (VAR) were called upon for several key decisions at the Confederations Cup in Russia on Sunday.

The first senior global tournament to have video technology for decisions other than goal-line calls saw it come into focus on the second day of action.

Chile left it late to edge out a dogged Cameroon 2-0, in an opening Group B clash that saw striker Eduardo Vargas have goals both ruled out and given by the video assistant.

"I think this system needs time. We are trialling the system right now and there are maybe doubts because we are used to other situations in football," said Chile coach Juan Antonio Pizzi.

"Maybe as we start getting used to it, it will get better. It is difficult for the players focusing in the game to absorb, and even if it is the right decision, it has an impact on their psyche."

A dramatic Group A game in Kazan that saw Hector Moreno head in an injury-time winner for Mexico also featured a goal by Luis Nani disallowed for offside on review.

Nani had converted from a rebound when Cristiano Ronaldo's volley rattled the crossbar in the first half, but the referee consulted the video official, who noticed that four Portuguese players had been offside in the passage of play before Ronaldo's shot.

Former Napoli striker Vargas had an eventful day, to say the least, as he struck the post in the first minute, saw a shot saved and then blazed an excellent chance over before he found the net in first-half stoppage time.

More than a minute had passed since Vargas' exuberant celebrations when the on-field referee signalled the goal had been chalked off. Initial replays appeared to show the forward level with the last defender, only for the technology that draws a line across the pitch to reveal half his head was in an offside position.

Confusion reigned in the stadium while Vargas and team-mate Arturo Vidal frantically pointed at the replays on the big screen to try and prove their point as the players walked off for the interval.

Then in the 81st minute, Vargas tapped home after Alexis Sanchez's shot was blocked by Cameroon goalkeeper Fabrice Ondoa. The 27-year-old was flabbergasted to see the linesman's flag raised, but video replays showed that Sanchez was onside in the build-up and Vargas' 34th international goal was given.

Under the VAR system, the referee can communicate with two video assistant referees with access to all camera channels.

REUTERS, AGENCE FRANCE-PRESSE