The game brought former Los Blancos manager, Jose Mourinho, back into battle with his old employers, and up against one of the players that served him during that time, Alvaro Arbeloa, who had replaced another of Mourinho's disciples in Xabi Alonso just a few weeks ago.
Third plays 29th
Far from being any love lost, however, Arbeloa was fulsome in his praise of his former coach, suggesting in his pre-match press conference that the 'Special One' set the blueprint for how to manage in modern football. Mourinho responded in kind, wishing the Spaniard well in his endeavours.
Ahead of the match, Real were third in the table and well inside the top eight cut-off for teams who would automatically qualify for the knockout stages of the competition.
The Eagles were 29th, amongst a cluster of teams on six points and would be eliminated without a big win, with goal difference being taken into account if needed.
In 2012, when the two sides last met, Benfica triumphed 5-2, though surely only the most fervent home supporter would've expected anything approaching a similar scoreline.
Centurion Otamendi
Real's Kylian Mbappe had been on fire during the competition, and had bagged a brace against Monaco in Los Blancos' 6-1 thumping of the French side last time out.
Juventus had seen off Benfica by a scoreline of 2-0, to ensure that the Portuguese giants had a mountain to climb in their final game, but Mourinho decided to stick with the same starting XI, meaning Nicolas Otamendi could make his 100th appearance in the Champions League.
A vibrant opening saw both sides get a player booked, whilst both the hosts and the visitors had three attempts at goal before there were even 20 minutes on the clock.
Leandro Barreiro wasn't overawed by the Spanish giants, and his four early tackles in this game were double that of any other player on the pitch.
Georgiy Sudakov was also making life difficult for Real, and by the time his 26th-minute effort had cannoned back off the woodwork, he'd made three chances in the game and kept the visitors on the back foot.
It's always Mbappe
All appeared in vain once Mbappe did what Mbappe does, and broke the deadlock with his 12th goal in this year's competition on the half-hour.
Only Cristiano Ronaldo for Real Madrid in 2013/14 (13) and Robert Lewandowski for Bayern Munich in 2019/20 (13) had scored more goals in the first seven games of a UCL campaign.
That didn't bode well for a Benfica side that had lost all four previous UCL games this season, that they'd conceded the opening goal in, and who were starting to get passed off the park by the incredible passing accuracy from the likes of Fede Valverde (95.5% completion) and Raul Asencio (96.8%).
Real's evident joy didn't last long, however, as Andreas Schjelderup lifted home spirits by equalising within five minutes.
The same player then had another effort cleared off the line, and Benfica managed three more attempts at goal despite Real's collective 66% possession.
Benfica lead against the run of play
With Jude Bellingham and Aurelien Tchouameni often found out of position and not having their best games, it didn't really come as a surprise when the latter gave away a penalty after his challenge on Otamendi.
In the arguments that followed, Asencio was booked for dissent, and that would come back to haunt him later in the day.
Vangelis Pavlidis made no mistake from the spot to put the cat amongst the pigeons at half-time.
The second half began at the same frenetic pace, and Benfica were soon further ahead through Schjelderup.
Whilst there has to be an acknowledgement that Real's defence isn't their first choice at present, managing only three successful tackles between them is a damning indictment on Dean Huijsen, Alvaro Carreras, Asencio and Valverde.
Not one of them was simply getting in where it hurts and providing the sort of defensive coverage Real are known for.
Bellingham more of a hindrance than a help at times
Bellingham may have felt he was helping by putting himself about, but the fact that he won just six of his 14 one-on-one duels suggests he was more of a hindrance on this occasion.
Arbeloa's response was to bring on Rodrygo and Eduardo Camavinga for Tchouameni and Franco Mastantuono, and it paid immediate dividends when Mbappe bagged his second just three minutes later.
The brace means he's just two goals from reaching 70 in the UCL, with plenty of time to join the centurions in due course.
Once again, Real were running rings around the hosts, with 70% possession in the opening 15 minutes of the second half, and it's not as if the likes of Fredrik Aursnes, Amar Dedic and Leandro Barreiro were playing badly, either.
Connotations started to become obvious
The Portuguese giants just weren't making many attacking inroads, and only four of Barreiro's passes were into the Madrid half, by way of example.
As the clock ticked down and the connotations of the result were becoming more obvious, needless fouls were being conceded by both sides.
Another triple change from Arbeloa appeared to be the right call as news made its way to the dugout that Real were out of the top eight because of results elsewhere.
The final 10 minutes saw some brilliantly chaotic play with both teams only needing one goal to secure the difference between success and evident failure.
The magnificent flying Trubin wins it with the last touch
Asensio's second yellow card in stoppage time saw him sent off, and subsequently ruled out of the play-off games, with worse to follow for Los Blancos as Rodrygo's dissent saw him given two bookings in four seconds and also ordered from the field.
With temperatures rising and a grandstand finish in prospect, there was still all to play for, but by now all of the action was down at the Real end.
Time was officially up when Benfica were awarded a free-kick outside the box after Bellingham was penalised for another foul.
Aursnes delivered the ball of his life that fell right on the head of his goalkeeper, Anatoliy Trubin, up especially for the corner, and he powered home to send the home fans crazy and Benfica into the playoffs along with Real.
It was the last touch of the match, and the 12th attempt on target from Benfica, a UCL high for them in 25/26.
