April 18 (Reuters) - Arsenal kept alive their slim hopes of securing a Champions League spot next season with a 2-1 Premier League victory at Middlesbrough on Monday that left the hosts in deep danger of relegation. A superb Alexis Sanchez free kick put the Gunners ahead three minutes before the break but Spanish striker Alvaro Negredo brought Boro level four minutes after the interval. German midfielder Mesut Ozil grabbed a close-range winner for Arsenal in the 71st minute. The result left Arsenal in sixth, seven points behind fourth-placed Manchester City who have played one game more. Boro are second bottom, six points adrift of safety with six games left. Arsenal manager Arsene Wenger made six changes to the team which had lost in humiliating fashion 3-0 to Crystal Palace last week and switched to a 3-4-3 formation, a new approach for the Gunners. "Sometimes when a team lacks confidence, changing the system helps the team to believe in something different," Wenger said. A low-key first half ended with Arsenal getting ahead when Sanchez showed great technique as he lifted the ball over a long wall and past motionless Boro keeper Brad Guzan. Boro responded positively, though, and their equaliser was perfectly executed, Stewart Downing racing down the right flank and delivering a pinpoint cross which Negredo met with a side-foot finish after losing his marker Laurent Koscielny. Middlesbrough went close to a second with a stooping Daniel Ayala header which Arsenal keeper Petr Cech saved well, allowing his defence to scramble clear. But Arsenal secured their first away win in five Premier League matches when Sanchez floated a ball into the box which Aaron Ramsey cleverly chested down to Ozil who made no mistake from close range. "I think we were focussed and committed and you could see that we did not play with full confidence during some moments in the game," Wenger said. "When you are in a lack of confidence situation it comes back slowly and only the results help," added the Frenchman. Arsenal face Manchester City on Sunday in the FA Cup semi-finals.