Mesut Ozil and Alexis Sanchez returned Arsenal to winning ways with a 2-1 win over Middlesbrough in a Premier League clash at the Riverside stadium on Monday.A fantastic free-kick from Alexis gave Arsenal a narrow half-time lead at the Riverside. Ozil settled matters after the break, latching on to a chest down by Aaron Ramsey to send a right-footed effort beyond Guzan, 21 minutes after Alvaro Negredo had brought the home side back on level terms.Arsene Wenger sprang a surprise by opting for a back three for the first time since his early days in charge. There were six changes to the side that lost at Crystal Palace last Monday, but it was the change in shape which was most noteworthy.Laurent Koscielny returned to skipper the side after missing two matches with an Achilles injury, alongside Gabriel and Rob Holding with Shkodran Mustafi unavailable due to a thigh strain.Petr Cech was also back from injury, starting for the first time since limping off during the first half of the defeat at West Bromwich Albion. Alex Oxlade-Chamberlain started on the right as Hector Bellerin dropped to the bench.Olivier Giroud was recalled up front, playing ahead of Mesut Ozil and Alexis Sanchez – Danny Welbeck missed out with a toe injury.First HalfBoth teams came into the match low on confidence, and that was reflected in the early exchanges, as neither side was able to take control. Alvaro Negredo tried a speculative effort from all of 40 yards, which was never troubling Cech, while Gabriel failed to make proper contact with an in-swinging corner at the other end.Both of Arsenal wing-backs were advancing into Middlesbrough territory at every opportunity, but they were unable to enjoy a sustained spell of possession. Aaron Ramsey and Alexis both had volleys saved in quick succession, but neither player was able to get enough power behind the shot. Those two sights of goal encouraged the Gunners and moments later Alexis looked to release Giroud inside the box, but there was just too much pace on the pass, and Brad Guzan smothered the danger.Guzan was left rooted to the spot shortly by Sanchez before half-time though after Granit Xhaka was brought down just outside the area, in a central position. The Chilean stepped up and whipped the ball up and over the heavily populated wall, and into the net for his 19th goal of the Premier League season.Second HalfThe second half started in the worst way possible. With the first real attack after the break, Stewart Downing swung in a deep cross and Negredo ghosted between Gabriel and Koscielny to poke home from close-range.Downing himself could have given the hosts the lead when Monreal's attempted clearance ballooned up in the area, but Downing's snap shot was wayward. It was back to square one, and Arsenal now had to weather some pressure from relegation-threatened Boro, as the fans found their voice.Cech made a terrific reaction save to deny Daniel Ayala from close range, and the rebound was eventually scrambled away.There were chances at both ends now. Giroud was well tackled Ben Gibson just as he was about to pull the trigger, while Oxlade-Chamberlain was the saviour moments later. Gaston Ramirez looked to be away in the Gunners half, breaking free when Monreal's shot was charged down while Boro were defending a corner. Oxlade-Chamberlain showed his pace though to race back and dispossess the advancing Ramirez.It was becoming an increasingly hotly-contested affair, but Ozil quietened the Riverside crowd with a great near post volley. Alexis floated in a cross which Ramsey chested straight into the path of Ozil, and he squeezed a right-footed first-time shot inside the post.It felt like a big goal in the context of this game. It certainly settled some nerves. Giroud could have wrapped up the win, but flashed a shot wide of goal, failing to wrap his foot around the ball after Alexis teed him up.Oxlade-Chamberlain also had a late chance snuffled out at the near post after another wonderful run forward but Arsenal had done enough.