London\'s leading clubs step up their battle for Champions League places this weekend, with Arsenal striker Theo Walcott saying defence holds the key to qualifying for European club football\'s leading tournament. Manchester United, already crowned Premier League champions, are assured one of the four spots on offer to English clubs while second-placed Manchester City are six points clear of a trio of chasing capital sides. Chelsea, currently third, are a point in front of Arsenal, with Tottenham Hotspur three points adrift of the Blues. Both Chelsea and Spurs have played one match fewer than the Gunners. Failure to qualify for the Champions League could have serious implications for any of the London trio, especially Arsenal who are bidding to play in the competition for a 16th straight season.If they miss out, speculation linking long-serving manager Arsene Wenger to a move to Paris St Germain is sure to intensify but Walcott said defending would be decisive in the race for a Champions League place. \"What it comes down to is that if you keep clean sheets, you are going to win games,\" Walcott said. \"In recent years we may have faded slightly at the end of games, with the pressure of being 1-0 up, but everyone here is very focused on doing their jobs correctly. \"If we all work hard for each other, then good things should follow.\" Arsenal will expect to keep a clean sheet when they travel to already-relegated London rivals Queens Park Rangers on Saturday. Tottenham, with Gareth Bale having been named Thursday as the Football Writers\' Association player of the year, barely a week after receiving the equivalent award from England\'s Professional Footballers\' Association, are at home to the Wales winger\'s former club, Southampton. \"I firmly believe that points will be dropped by all of these three teams that are competing -- four if you include Everton, who are in the frame because they are still in with a shot,\" said Tottenham manager Andre Villas-Boas as he tried to minimise the potential impact of a defeat by the Saints. Chelsea, who advanced to the Europa League final after a 3-1 second leg win over Basel at Stamford Bridge on Thursday, travel to Old Trafford.Everton, three points adrift of fifth-placed Tottenham, will go in search of their first league win at Anfield since 1999 when they face Liverpool in the Merseyside derby. \"The most important thing is to get into Europe,\" said Everton\'s Steven Pienaar. \"I know at this stage it is difficult but we just want to win the games and see how far we go,\" the South Africa midfielder added. \"You don\'t know what is going to happen on top of us. Maybe one of the teams can lose all their games and we win all ours.\" While QPR and bottom of the table Reading have already been demoted, the fight to avoid finishing in the remaining relegation place, currently occupied by Wigan, is arguably even more intense than the contest for European football. There are five clubs within seven points of FA Cup finalists Wigan, away to West Brom on Saturday. Newcastle, who conceded six goals against Liverpool last week, are away to West Ham when Aston Villa travel to manager Paul Lambert\'s former club Norwich. Sunderland, who themselves let in six against Villa, will look to return to winning ways against Stoke on Monday. Fixtures (1400GMT unless stated) Saturday: Fulham v Reading, Norwich v Aston Villa, Swansea v Manchester City, Tottenham v Southampton, West Brom v Wigan, West Ham v Newcastle, QPR v Arsenal (1630GMT) Sunday: Liverpool v Everton (1230GMT), Manchester United v Chelsea (1500GMT) Monday: Sunderland v Stoke (1900GMT) From: AFP