Arsene Wenger has admitted Chelsea's defeat at the hands of Tottenham has boosted Arsenal's hopes of getting back in the race for the Premier League title.
Arsenal's title ambitions were dealt a blow when they had to settle for a 3-3 draw at Bournemouth on Tuesday, but Chelsea's 2-0 setback at White Hart Lane 24 hours later - their first defeat after 13 consecutive wins - keeps Wenger's men within eight points of the leaders.
"It looks like Chelsea are still quite comfortable but when you are interrupted in a series of wins, it always raises hope for others. It means you have to restart again," Wenger said at a news conference.
"I think it is an open league.
"The second part of the championship starts now. We know that January until May is the moment of truth for everybody. Who will come out of this race on top? It is very difficult to predict at the moment."
Arsenal are fifth in the table and Wenger has acknowledged a top-four finish - and Champions League qualification - is by no means a guarantee.
"The battle for top four is tough for everybody," he added.
"But at the start, you want to win the league and give absolutely everything to do it.
"But I agree, every year you have to function exactly the same, no matter who you are. First, get 40 points. After, fight to be in the top four and possibly fight to win the league."