Postpublished at 16:26 British Summer Time 24 May 2015
A round of applause for Theo Walcott as the hat-trick hero departs, to be replaced by Olivier Giroud. Which of those two will start against Villa in the cup final next week, then?
Arsenal XI: Ospina; Bellerin, Mertesacker, Gabriel, Gibbs; Cazorla, Coquelin; Wilshere, Ozil, Sanchez, Walcott.
West Brom XI: Myhill; Dawson, McAuley, Olsson, Lescott; Fletcher, Yacob, Morrison; McManaman, Berahino, Brunt.
Mike Whalley
A round of applause for Theo Walcott as the hat-trick hero departs, to be replaced by Olivier Giroud. Which of those two will start against Villa in the cup final next week, then?
Well. Is this the start of a fightback? Gareth McAuley climbs to head in a corner, with Arsenal keeper David Ospina making a bit of a dog's dinner of it, to be honest. It's the Albion centre-back's first league goal since December 2013.
There's a third and final West Brom substitution in the aftermath of that goal, as Chris Baird comes on for Claudio Yacob. I suspect if Tony Pulis had been allowed 11 substitutions, he would have used the lot after that first half.
Arsenal don't, for now, look to be settling for four. Santi Cazorla's curling shot is pushed aside by Boaz Myhill, and Theo Walcott puts the loose ball over on the stretch. Tony Pulis makes another substitution, taking off Callum McManaman and bringing on Craig Gardner. The words "deckchairs" and "Titanic" spring to mind.
Arsenal continue to pass the ball around neatly in the opening minutes of the second half. Tony Pulis responds by bringing off Jonas Olsson, a defender, and putting on Victor Anichebe, a striker. Well, Albion have nothing to lose. They might as well go for the 4-4 draw now.
Theo Walcott's last hat-trick for Arsenal, by the way, was in that extraordinary 7-3 Premier League win over Newcastle in December 2012.
Former Arsenal defender Martin Keown
Final Score
"Theo Walcott has looked absolutely rapid today and it must be on Arsene Wenger's mind about whether or not he should start him next week."
We're back under way at Arsenal. I dread to think what Tony Pulis's half-time team talk was like.
Gary Lineker
MOTD presenter
Theo Walcott has scored a hat-trick in 33 minutes, the fastest in the Premier League since.....last week.
A one-sided first half in numbers.
MOTD's John Motson
at Emirates Stadium
"That was one of the best and most eventful first halves Arsenal have produced this season."
Arsenal could have had more in this first half as well. Jack Wilshere has a shot blocked by a desperate Albion challenge. And as brilliant as the Gunners have been, this is a desperate Albion performance.
MOTD's John Motson
at Emirates Stadium
"Arsenal have now scored 105 goals this season, and there have been 21 different scorers."
I cannot believe this is the same West Brom starting line-up that beat Chelsea 3-0 six days ago. And yet it is.
Theo Walcott again! It's as if West Brom have never heard of the England forward, given the amount of space he's getting. Walcott runs at the Albion defence again and drives a shot that Boaz Myhill pushes around the near post.
What a superb day this is turning out to be for Theo Walcott. Before today, he had scored three goals all season. Now he has three in 37 minutes.
It's another lovely Arsenal move, with Jack Wilshere and Alexis Sanchez combining, before Santi Cazorla rolls the ball across goal for Walcott to tap in. Ridiculous game, this.
George Jenkins: Crazy last day of the season - keep them coming, Arsenal!
Harry Partridge: Arsenal haven't had an injury crisis for a few months. Shad Forsythe [the head of athletic performances] has done great work and could help them win the title next year.
Abdul Said: Let's see who will start the FA Cup final, Giroud or Walcott, and who will be the main striker next season.
Arsenal haven't scored for more than 10 minutes now. I'm classing this an official goal drought.
Per Mertesacker gets in front of his marker to touch a Santi Cazorla free-kick towards goal, but Boaz Myhill gathers.
I'm thinking back to Arsene Wenger's pre-match quote about his team's recent lack of goals: "The best way to approach it sometimes is not to talk about it."
Hard to argue, Arsene. Hard to argue.
Former Arsenal defender Martin Keown
Final Score
"Walcott has gone through a couple of challenges there where before he might have been worried coming back from the injury he has had. This is him staking his claim to start in the FA Cup."
Now Jack Wilshere has a sight of goal on the edge of the penalty area, and fires straight at Boaz Myhill. This could end up any score. Well, any score greater than 3-0.
Theo Walcott is tearing West Brom to pieces. Played in by Alexis Sanchez, he gets in behind the visitors' over-stretched defensive pair of Jonas Olsson and Gareth McAuley, and whips in a shot that keeper Boaz Myhill does well to push aside.