Liverpool beat Newcastle in their last match, 4-0.
The reigning champions trail leaders Liverpool by seven points and were overtaken by Tottenham after losing 2-1 at Leicester on Wednesday. Salah looked to shoot from the edge of the box only for Granit Xhaka to get a block in and Stephan Lichtsteiner to hit the loose ball straight at Shkrodan Mustafi.
The Brazil international's next 90 seconds later required no such element of luck.
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Juan Mata says now is a time for optimism at Manchester United , with Ole Gunnar Solskjaer having taken over from Jose Mourinho . They are sixth in the Premier League, eight points behind Chelsea in fourth.
Former Manchester United and Manchester City midfielder Owen Hargreaves fears for Liverpool if Salah or Mane gets injured though. Robertson plays a wonderful ball over the top for Salah who side-foots it across to Mane and he pokes home for Liverpool's third. Sokratis likes players tight to him so he can rough them up.
Leno had to make a save from Fabinho after a clever flick from Salah set up another chance, so Arsenal could not complain too much about another soft penalty bringing a fifth Liverpool goal.
It capped a spell reminiscent of the encounter in February 2014 when the Gunners were blown away in the opening 20 minutes of another 5-1 defeat. "We were aware of the Tottenham result ahead of this game, but we can't allow that to affect us". So many ankles broken.
Liverpool defend their leadership at home to Arsenal, who have become rather inconsistent in recent games and one of the main talking points will be whether the talented, but over-mercurial Mesut Ozil will start for the visitors after being replaced for "tactical reasons" in their draw at Brighton on Boxing Day.
Liverpool were given another penalty midway through the second half when Sead Kolasinac was adjudged to have pushed Dejan Lovren.
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