London - Per Mertesacker remains confident Arsenal can overcome north London rivals Tottenham Hotspur this weekend although Alexis Sanchez will be absent from the Gunners' line-up.
Sanchez has been ruled out of Saturday's trip to White Hart Lane after failing to recover from the hamstring that kept him out of Arsenal's comfortable 5-0 victory over Aston Villa last weekend.
The loss of the Chile forward is a blow to Arsene Wenger's side as they attempt to repeat their success in last season's corresponding fixture in March.
While Arsenal make the short journey to the home of their nearest neighbours and fiercest rivals full of confidence after an impressive recent run, Spurs are also heading into the game in good form.
Gunners centre-back Per Mertesacker knows Mauricio Pochettino's men will present a testing challenge as Wenger's side attempt to extend their run of five straight victories.
But the Germany international believes the key will be whether Arsenal can maintain their defensive solidity that has produced four clean-sheets in their last five games and left them level on points with fourth-placed Southampton heading into this weekend's round of Premier League fixtures.
"We know from recent years that defensive unity is vital especially against our north London rivals, so we have to be really cautious on the defensive front," Mertesacker said.
"We did very well last season, as we scored very early and then defended well until the end, so it's going to be the target for this year."
Arsenal have reacted well to the New Year's Day defeat by Southampton and their sequence of victories have moved the Emirates Stadium club back to the brink of the top four and in the fifth round of the FA Cup.
Only goal difference is keeping Arsenal out of the Champions League places at present, with Tottenham one place and two points behind.
Kick-off is at 14:45 on Saturday.