A brilliant late strike from Ferland Mendy gave Real Madrid a 1-0 win over 10-man Atalanta in Bergamo as the hosts saw Remo Freuler controversially sent off early on.
An open beginning to the first leg was marred by a debatable refereeing decision as Freuler was shown a harsh straight red for bringing down Mendy on the edge of the box.
It was adjudged the Swiss midfielder denied the French left-back a clear goalscoring opportunity. Ultimately it was a questionable decision from German referee Tobias Stieler with other Atalanta defenders in the vicinity.
Sterling may be denied Real Madrid move as he prepares for exit - Paper Round
With Real eager to capitalise on their man advantage, stand-in false nine Isco and Luka Modric both had efforts on goal before Casemiro missed their best chance in first-half injury-time.
The Brazilian - who scored an aerial winner against Real Valladolid last Saturday - guided his point-blank header from a delightful Toni Kroos corner straight into the body of goalkeeper Pierluigi Gollini.
The second half was a tale of Real Madrid dominating possession but struggling to break down a compact, resolute Atalanta defence. Modric saw two half-chances go wide while Marco Asensio had a free-kick comfortably saved.
But finally, in the 86th minute, the deadlock was broken with Bendy firing a vicious right-footed strike from the edge of the box into the bottom corner.
TALKING POINT - No Benzema = no strategy
Although it was partially commendable Real won the game without eight first-team players, they were sorely lacking their talisman Karim Benzema, who has 17 goals this season.
With Isco playing as the lone frontman, the La Liga champions were bereft of ideas going forward against 10 men for most of the match. It took a wonderful right-footed strike from their left-back to make the difference.
When Real's second highest scorer this season is holding midfielder Casemiro on six, it was again made glaringly obvious that Los Blancos urgently need to sign a new striker.
'Bad performance, good result' - Zidane on Real's win over Atalanta
MAN OF THE MATCH - Rafael Toloi
Atalanta's captain Toloi led by example on a night where they simply could not leak goals while hampered by being a man down.
The Brazilian-Italian was aerially dominant and threw his body in the way of Madrid's close-range efforts. He and his Atalanta team-mates will feel hard done by not to go into the second leg on level terms.
Atalanta: Gollini (7), Toloi (8), Romero (7), Djimsiti (7), Maehle (6), De Roon (6), Freuler (3), Gosens (6), Pessina (6), Zapata (6), Muriel (6)
Subs: Pasalic (7), Ilicic (6), Malinovsky (N/A), Palomino (N/A)
Real Madrid: Courtois (6), Vazquez (6), Varane (6), Nacho (7), Mendy (8), Kroos (6), Casemiro (7), Modric (7), Asensio (5), Vinicius (6) Isco (5)
Subs: Mariano (5), Arribas (N/A), Duro (/A)
17' - RED CARD! Freuler is shown a straight red! Isco slipped through an onrushing Mendy who was bombing into the box after some wonderful one-touch football. Was the Swiss midfielder denying the left-back a clear goalscoring opportunity? Probably not as there were other defenders around. Nevertheless, Atalanta are down to ten and Real Madrid have a free-kick in a dangerous position.
45' - SO CLOSE!! A delightful cross from Kroos is met by Casemiro but his point-blank header hits Gollini and goes out! That was the best chance of the half by a mile.
48' - CHANCE! Modric gets a shot away from just inside the Atalanta box in a tight space with the outside of his right boot. It takes a slight deflection and the ball spins agonisingly past the post!
86' - GOAL!! Finally Real Madrid get their goal and it is Mendy with a sensational strike! The corner comes out to the left-back who shifts the ball to his right foot and superbly bends it past Gollinig into the bottom corner! Zidane loved that! Finally the breakthrough!
The future of El Clasico? It’s in the midfield
Haaland demands £30m-per-year wages as clubs prepare summer bids - Paper Round