Just when things were looking good for Arsenal, the Gunners failed to go clear at the top of the Premier League after a goalless draw against Middlesbrough on Saturday.
They have sparkled in recent weeks but were lucky to escape the Emirates with a 0-0 rather than a defeat as Boro created their fair share of chances.
Significantly, Santi Cazorla was missing from the line-up due to an Achilles injury sustained in the 6-0 win over Ludogorets in the Champions League on Wednesday.
We have already seen how vital he is to the Arsenal cause, both through his absence in the second half of last season and at the start of this one.
In comparison to the deep midfield pair that started against Middlesbrough, the Spanish playmaker provides more guile and incision than Mohamed Elneny and Francis Coquelin respectively.
They just appear more fluid and on the pace when he is in the centre of the park, dictating the pace and the flow.
And that takes the pressure of Mesut Ozil in terms of the necessity to drop deeper.
Unfortunately for Arsene Wenger, Olivier Giroud was unavailable as well, as he would have provided the aerial option they were missing as they pinned Boro back and tried to find a way through.
Fortunately, though both are likely to be back with Cazorla more fundamental and Giroud a good option to have if another direction is sought.
As he told the Arsenal website, Wenger more or less confirmed that both players won't be out for too much longer.
West Bromwich Albion's Gareth McAuley (second right) scores his side's first goal of the game during the Premier League match at Anfield, Liverpool. Picture by: Dave Howarth / PA Wire/PA Images
But he also made pertinent point, regarding the importance of Cazorla to their hopes: "You miss always, of course, Cazorla. At home he is from deep midfield into the final third, his pass is always quick and accurate."
Meanwhile, also on 20 points are Liverpool as their 2-1 win at home to West Brom. It is the time of game and opposition that can cause a slip-up with Tony Pulis teams organised and set up to frustrate.
With Liverpool in possession, the Baggies were always going to be that tougher to break down, especially with both widemen sitting deep on the toes of their full-backs.
That's why the transition on the counter was so important for Liverpool and it's how the all-important opening goal came thanks to some great presence of mind from Philippe Coutinho.
West Brom were not going to be as stable defensively when Liverpool won the ball back and moved quickly from back-to-front.
However, one concern emerges for Liverpool and that is defensive set-pieces. When they beat Swansea a few weeks ago, the Reds had to overcome the concession of a Leroy Fer goal from a corner.
West Brom's ultimate consolation goal late on came from the same source.
An in-swinging Cazorla free-kick to Calum Chambers saw Liverpool concede a third against Arsenal on the opening day.
Ireland's David Meyler smashed in from a corner as Hull City lost 5-1 at Anfield in September.
In tighter matches than Saturday's fixture - Liverpool should have scored more than two - a mistake from a set-piece will be of even more worrying value.
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