"We've had the opportunity to use it, it has been used very effectively and we've come out with the right outcomes".
Welbeck's challenge in the penalty area on Cesc Fabregas was referred to Video Assistant Referee Neil Swarbrick by Martin Atkinson but after a lengthy delay the decision was no penalty.
VAR can be used by referees for match-changing decisions relating to the awarding of goals, penalties, red cards and for cases of mistaken identity.
"That is a little bit longer than we have done in training", said Riley.
And Gunners striker Welbeck added: "I didn't know the VAR referral was for that incident".
"It's going to take us time".
Bristol City loan Liverpool winger Ryan Kent
Kent started just one Bundesliga game during almost five months at the club and was recalled by Liverpool earlier this month.
"We're talking around that, reviewing both games this week and coming up with some ideas for next week to make that more effective". Some television replays were initially unclear whether the ball brushed against Murray's arm before falling into the net.
"When you get a team in the last five minutes, and you take a corner quick and another one, and so I was like, "hmm".
If Chelsea beat Norwich, their tie with Newcastle United - also on BT Sport 2 - could be another VAR game the following afternoon. "If the referee has made a wrong decision and VAR can quickly correct that and get the right outcome then the game will benefit".
"It's the result of a lot of testing having been done already in a non-game situation, which has really refined this referee to technology interface".
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