Paul Merson believes Arsenal boss Mikel Arteta made a mistake in starting Bruno Guimaraes against Brighton.The Brazilian midfielder struggled – along with the rest of his team-mates – as the Gunners were soundly beaten 3-0 on the south coast.’I’d like to ask Mikel Arteta what his thinking was behind playing Bruno Guimaraes over Myles Lewis-Skelly,’ wrote former Arsenal forward Merson in his Sky Sports column.’I don’t know if he thought it would be a nice football match, that Brighton would be tired after coming from 2-0 down against Manchester United on Wednesday?’It just didn’t work. Arsenal got outrun, they got overpowered in midfield, they got ripped to shreds.’Bruno’s a good footballer. If you’re playing a low block, I don’t see the problem in playing him. When you’re going to dominate the ball, there’s no-one like him when you have time. He’s a good player and passer – and he’s very intelligent. Guimaraes struggled – along with the rest of his team-mates – as the Gunners were soundly beaten 3-0 on the south coast’I just wonder if Arteta was sitting on the coach on the way back thinking “I’ve got that one wrong”.’When Bruno came on as a sub against Aston Villa a few weeks ago, he was outstanding. He could just keep the ball, pop it around, play one-twos and play the game at his tempo. That would have been a better idea.’I’m not blaming Bruno for Arsenal losing, absolutely not. I just didn’t know why Arteta had to change the team in a very difficult game.’Saturday’s defeat left the defending champions second in the table after Manchester City followed up by beating Sunderland on Sunday to clinch the top spot with a three-point margin.