Just in case Arsenal needed any further evidence why they have to keep hold of Alexis Sanchez beyond this summer, it was provided against Sunderland.The Gunners ensured the race to finish in the top four will go down to the final day with a 2-0 victory over the already relegated Black Cats, courtesy of a Sanchez brace.It was beginning to look like it was going to be one of those frustrating nights at the Emirates with the scores still level heading into the second half.Arsenal had looked in complete control of proceedings but the lack of a breakthrough was starting to make some of the sparsely situated supporters feel restless.They did eventually open the scoring when that man Sanchez stepped up to add the finishing touch to a fine team move in the 72nd minute.Cue a giant sigh of relief all around the Emirates.He added a second just a few minutes later which effectively secured the three points.Meanwhile, it was a particularly frustrating day for Mesut Ozil.Yes, he may have got the assist to Sanchez's first but he cut a forlorn figure for most of the game - even pushing and kicking the ball at Bryan Oviedo when the Sunderland full-back didn't step back from a free-kick.And Arsenal fans were even less impressed by the level of his work rate in the final stages of the game.As you can see in the video, the Black Cats have the ball at the back when Sanchez comes sprinting in to close them down.The Chilean's pressure forces the pass out wide to be rushed and misdirected.Oh, and who's that at the corner of the screen making absolutely no effort to retrieve possession? Yep, Ozil.He would have quite comfortably reached the ball before Sunderland had he not been walking back.Here's how Gunners supporters reacted on Twitter:

If it boils down to Arsenal keeping only one of Ozil and Sanchez this summer, on that evidence alone we know who'd we prefer...