When Jurgen Klopp is enjoying a well-earned sabbatical, this is the kind of occasion the Liverpool manager will surely miss: two first-rate teams, trading blows at a frantic pace, with the league title on the line.
They cost Liverpool the game and might just cost Klopp another league title, as Arsenal's 3-1 win moved them to within two points of the league leaders.
Alisson's first error was the more significant, with the second coming in stoppage-time after Ibrahima Konate had been sent off and Liverpool hope was fading.
As Van Dijk shepherded a long ball towards the onrushing Alisson in the 67th minute, the goalkeeper kicked clean air, allowing Gabriel Martinelli to gratefully side-foot into an empty net.
It will be little consolation to Klopp that Liverpool's equaliser on the stroke of half-time was similarly comic, Gabriel slapping the ball into his own net to cancel out Bukayo Saka's opener.
Leandro Trossard fired through Alisson's legs for Arsena's third, another bad moment for the visiting 'keeper.
These are the moments on which seasons hinge, and Arsenal will now have belief and momentum, their mid-winter blip firmly in the rearview mirror.
Klopp's impending departure is an opportunity for the Gunners long-term but Arteta's side look ready now.
The only concern for Arsenal going forward was Saka hobbling off in the second half, appearing to hold his leg, after a collision.
But as the Emirates danced after the final whistle, there was a palpable sense that Arsenal are coming to the boil nicely.
The pace was predictably frenetic from the off, Saka and Martinelli looking in the mood.
The pair combined for the game's first big chance. Raya's long throw set Martinelli clear on the halfway line and the Brazilian sprinted away from Konate before digging out a cross which Saka could only brush with his head.
Moments later, the England winger was knee-sliding towards the corner flag in celebration. Martin Odegaard's killer first-time pass set Havertz clear through a collosal parting in the Liverpool defence.
His tame shot was easily saved by Alisson but the rebound fell to Saka, who took a touched and rifled into the unguarded net.
Arteta celebrated extravagantly, punching the air and roaring his approval to the bench.
Odegaard's shot from the edge of the box was blocked after Alexander-Arnold was pressed into a mistake and Martinelli had the beating of the full-back, often forcing Konate over to cover. More pressure allowed Gabriel to dig out a shout from the edge of the box which extended Alisson.
Arsenal were good value for their lead as half-time approached but deep into the three minutes of stoppage-time, they conceded poorly.
The goalkeeper never came and Diaz was able to wriggle around Saliba and dig out a cross, which Gabriel spun and diverted over the line with his hand. Liverpool were level without having a shot on target and the Emirates suddenly felt nervous.
From an Arsenal perspective the goal was a mess all-round, with Saliba the most culpable for failing to clear and it was a dreadful time to concede, particularly as Liverpool tend to improve in the second half.
But the game remained finely-poised and Odegaard flashed a deflected effort into Alisson's side-netting at the other end.
The teams continued to trade opportunities, Saka and Diaz both shaping for curlers and Arteta furiously appealing for a penalty when Mac Allister raced back to tackle Havertz.
A goal was coming but no-one saw the winner unfolding until Martinelli was gleefully rolling the ball into an empty net after a chaotic mix-up between Van Dijk and Alisson.
Liverpool were not done yet and Mac Allister twice went looking for an equaliser, his second shot creeping just wide on the volley.
Konate's red card, both bookable offences for grappling with Havertz, seemed to sap the life from the visitors, however, and Arsenal soon had the result wrapped up from Alisson's second error of the night.
Trossard turned away from Elliott and bore down on the goal, the angle still too tight for major concern. But the Belgian's tame shot went straight between Alisson's legs, and the Emirates could finally erupt in celebration and relief.
Arteta wheeled up and down the touchline in a wild victory dance, sensing that Arsenal are firmly back in the title race with a landmark win.