It is the start of judgment year. Arsene Wenger enters the final season of his contract with Arsenal facing a greater challenge than ever before to retain their top-four status.
Jurgen Klopp begins the first campaign of a new six-year deal having rightly escaped censure for Liverpool's joint-lowest finish since 1962. They came eighth in May, in a season of two managers, two Cup finals and 63 games.
Now Klopp can be assessed, with his team, his signings and his demanding pre-season programme. Liverpool need to be hugely fit to perfect the German's gegenpressing game and arrive at the Emirates Stadium having played nine friendlies.
They have posed questions - is the real Liverpool the team that overwhelmed Barcelona 4-0 or the one that lost to Mainz by the same scoreline - and showcased signings.
There should be competitive debuts tomorrow. Ragnar Klavan, Georginio Wijnaldum and the explosive, unpredictable Sadio Mane, who will add pace and a goal threat from the right, are likely to make their Liverpool bows.
In contrast, Arsenal have only one senior signing in Granit Xhaka. If a second recruit, Rob Holding, starts, it will be an indication of unexpected problems in the Gunners' rearguard, with the 20-year-old defender relegated to League One with Bolton last season.
But Arsenal appear unready. As is his wont, Wenger gave an extended break to players with busy summers, but their Euro 2016 semi-finalists included Olivier Giroud, Mesut Ozil, Aaron Ramsey and Laurent Koscielny. The Welshman may be the only starter among them.
With Danny Welbeck, Per Mertesacker and Gabriel Paulista injured, Arsenal are short in both the middle of defence and attack. It illustrates that Wenger requires another centre-back and striker. Targets such as Shkodran Mustafi and Alexandre Lacazette have proved elusive so far.
At least, in true Wenger-esque fashion, he has a surfeit of progressive midfielders.
It will be instructive if Alex Oxlade-Chamberlain, arguably Arsenal's player of pre-season, or Alex Iwobi, who could be set for a breakthrough year, start.
Either, should he be on the right wing, must test what seems to be Liverpool's Achilles heel: the left-back. Alberto Moreno was abject in both the League Cup and Europa League final. Midfielder James Milner has filled in ably in friendlies, but remains a fitness doubt.
Yet, even though striker Daniel Sturridge is also struggling with a hip problem that kept him out of their last two friendlies, the sight of Arsenal's makeshift centre-back partnership should underline that Liverpool have a wonderful chance.
As the Reds play their first three games away and as Arsenal travel to Leicester next, each run the risk of becoming a slow starter if they lose.
It is too soon to brand it a must-win game for either, but it is important. At least the attacking philosophies of Klopp and Wenger, which produced a pulsating 3-3 draw in January, mean it should be watchable.
But they will not be judged solely on the entertainment factor.
ARSENAL V LIVERPOOL
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