Arsenal 2, West Brom 0: Full time analysis
West Brom swung a free-kick into the area which Szczesny dropped under pressure at the far post from Leon Barnett, but fortunately Kieran Gibbs - who had played in the Champions League semi-final defeat to Manchester United last season - was on hand to clear.
West Brom continued to look dangerous on the break, with Thomas' run down the left forcing Szczesny to make an important block.
However, the 26-year-old was shown a straight red card in the 37th minute after he clashed with Wilshere, before then slapping the midfielder in the face while he was on the floor.
Cox also went into referee Lee Mason's book for his protests.
Cox headed over for the first real chance of the second half when well placed in the six-yard box before Wenger made a change in the 58th minute.
Mexican striker Vela and Randall came on, replacing Sunu and Francis Coquelin.
The game continued to be scrappy, as the visitors closed down the space quickly.
It took a moment of Premier League quality from Vela to finally help break the deadlock.
The 19-year-old showed great close control to create space for a shot from the edge of the penalty area, which Kiely palmed wide, and Watt followed up to smash in his first senior Arsenal goal.
The Mexican then got the goal he deserved after 75 minutes.
Randall's 20-yard chip came back off the underside of the bar - and Vela was alert enough to get in between Barnett and Kiely before knocking the ball over the line.
The Baggies missed the chance to pull a goal back with 10 minutes to go when substitute Chris Wood fired wide at the far post - which just about summed up their night.
end
