Noussair Mazraoui again proved to be Ajax's man for the big Champions League occasion as his injury-time strike sunk Benfica 1-0 in Amsterdam.
An absorbing encounter looked set to end goalless after Benfica centre-back German Conti and goalkeeper Odisseas Vlachodimos made incredible last-ditch interventions to keep Kasper Dolberg and Donny van de Beek at bay respectively.
But right-back Mazraoui, who scored in the 1-1 draw against Bayern Munich last time out, lashed a deflected effort past Vlachodimos at the death to send the Johan Cruyff ArenA into raptures.
The result leaves Erik ten Hag's side dead level with Bayern at the Group E summit after three games, with both teams on seven points and holding an identical goal difference.
Ajax keeper Andre Onana was busy in the opening five minutes, getting down sharply to his right to deny Rafa Silva and Haris Seferovic.
The hosts established control after a frenetic opening and Vlachodimos was out quickly as he thwarted Dolberg on the end of Hakim Ziyech's slide-rule pass.
Olympiacos continued to threaten but needed an astonishing goal-line clearance from Conti – spinning and produce an acrobatic overhead kick as Dolberg's effort appeared certain to loop into the net – to maintain parity at the break.
A pleasing ebb and flow continued during the second period as the twinkle-toed Ziyech sent a 25-yard shot narrowly wide in the 58th minute, immediately preceding an encouraging spell of Benfica pressure.
There were Benfica heroics to match Conti's with 17 minutes to play, as Ziyech dragged the ball back and teed up Van de Beek to crown a sweeping Ajax move.
A goal looked inevitable but Vlachodimos had other ideas as he thrust out a strong right arm to produce a stunning reaction save.
When Mazraoui struck at the last, however, he was powerless to intervene.
What it means: Benfica must respond
Benfica's players looked understandably crestfallen at full-time and, with a four-point gap now opened up between themselves and Ajax, victory for Rui Vitória's side when the team reconvene in Lisbon in matchweek four is a must.
Ziyech sparkles amid Ajax stylist
From the sought-after Frenkie de Jong to the experienced Lasse Schone, Ajax are not short of players who can pleasingly negotiate 90 minutes as if in carpet slippers. Nevertheless, the virtuosity of Morocco international Ziyech stood out. His mesmeric footwork and inventive play sent many a Benfica defender darting down blind allies.
Onana sets pulses racing
Ajax's goalkeeper certainly does not lack for bravery or sharp reflexes but his eagerness to extend his involvement across his penalty area can certainly lead to some nervy moments for the Amsterdam faithful. Onana's second half collision with Benfica captain Jardel left him requiring treatment and could have cost his team.
What's next
Feyenoord are up at the Johan Cruyff ArenA on Sunday for what is always likely to be a feisty encounter, while Benfica head to Primeira Liga draw specialist Belenenses.
