Arsenal's Per Mertesacker London - Arab Today Arsenal defender Per Mertesacker has warned his side's Premier League title rivals the best is still to come from star midfielder Mesut Ozil. Arsene Wenger's side head to Cardiff on Saturday looking to extend their lead at the top of the table before the rest of the title challengers play on Sunday. A win would move the Gunners seven points clear of second placed Liverpool, who face Hull 24 hours later, and Mertesacker is confident they will do just that if Ozil is at his best in Arsenal's first league fixture at Cardiff since 1961. After a brilliant start to life in England following his club record £42 million move from Real Madrid on transfer deadline day, Ozil has produced a few under-whelming displays of late. He missed a penalty in Tuesday's Champions League win over Marseille, but rebounded to provide an assist for Jack Wilshere to score Arsenal's second goal and Mertesacker believes Ozil will quickly silence any critics. "Mesut has made good progress," Mertesacker said. "He was always a threat against Marseille and he never gave up after the penalty that he missed. "We are delighted with him, especially in the transition from defence to offence, when he is always a threat. "He can play the balls, he is the one who always goes deep all of the time. He is in good form and I think we will see more. "Sometimes he looks like his head is going down, but we said at half-time that we do not care about the missed penalty. We just go on and that is what he did." On Sunday, Liverpool will look to keep pace with Arsenal when they visit the KC Stadium and Reds midfielder Jordan Henderson knows his team are under pressure to take advantage of a relatively easy run of fixtures. After facing Hull, Brendan Rodgers' team play Norwich and West Ham and Henderson said: "We are second in the league and we have to make sure we continue in the way we have started the season. "We have had a couple of difficult away games. I think we're doing okay but we can still improve and keep pushing on." Third placed Chelsea, behind Liverpool on goals scored, host Southampton, with Spanish defender Cesar Azpilicueta admitting Jose Mourinho's team need to bounce back from a lacklustre display in their midweek loss at Basel in the Champions League. "Sometimes it happens," Azpilicueta added. "One day you play really well, three days later really bad. "We don't want to have this kind of movement in our performance because it's important to keep your balance, to play well every day. "Sometimes we don't keep the level to win every game. For Chelsea that cannot be possible." Free-scoring Manchester City will look to continue their goal spree when they meet Swansea at Eastlands. Manuel Pellegrini's fourth placed team have scored 22 goals in their last four home matches, but French midfielder Samir Nasri has warned his team-mates to focus on defence as well after a sloppy Champions League showing in a 4-2 win over Czech minnows Viktoria Plzen. "We are scoring a lot of goals but we cannot score four goals every game," Nasri said. "We need to improve how we defend as a team." Also on Sunday, champions Manchester United will travel to Tottenham for a clash between two teams who have under-achieved so far this season. United are seven points behind Arsenal after slipping up against a series of supposedly inferior opponents, including a 2-2 draw at Cardiff last weekend. David Moyes' men looked more like their dominant selves in a 5-0 rout of Bayer Leverkusen on Wednesday and they will expect to keep the pressure on Tottenham manager Andre Villas-Boas, with some reports claiming he is in danger of being sacked after a 6-0 thrashing at City on Sunday left them languishing in ninth place. Meanwhile, Crystal Palace's new manager Tony Pulis starts his reign with a crucial trip to fellow strugglers Norwich. Fixtures (1500GMT unless stated) Saturday Aston Villa v Sunderland, Cardiff v Arsenal, Everton v Stoke, Newcastle v West Brom (1730GMT), Norwich v Crystal Palace, West Ham v Fulham Sunday Chelsea v Southampton (1610GMT), Hull v Liverpool (1405GMT) Manchester City v Swansea (1610GMT), Tottenham v Manchester United (1200GMT) Source: AFP