PARIS >> Trailing until the 89th minute against Sporting Lisbon, Real Madrid was reminded that becoming the first club to retain the trophy in the Champions League era won't be an easy task.
The 11-time champions needed a late winner from substitute Alvaro Morata to prevail 2-1 in their opening game in the competition on a Wednesday night also marked by Premier League champion Leicester's maiden Champions League win.
Playing against his former team, Cristiano Ronaldo was on the score sheet at Santiago Bernabeu stadium as he leveled with one minute left from a free kick before Morata's winner in added time. But the Portugal star was unable to match Sergio Aguero, who netted a hat trick with Manchester City.
After a one-year absence in the tournament, Dortmund celebrated its return by putting six goals past Legia Warsaw, while French clubs Monaco and Lyon made both winning starts.
Here's a roundup of all the action on Wednesday:
Thrashed by Tottenham 4-1 at White Hart Lane last season in Europa League, Monaco took its revenge on Europe's biggest club stage with a 2-1 win at Wembley.
The match was moved to England's national stadium because of construction work at Spurs' home ground and drew 85,011 fans, a club-record home attendance and a record for an English club.
The crowd did not impress the French league leaders as Monaco playmaker Bernardo Silva, who impressed throughout, opened the scoring after only 15 minutes before Thomas Lemar doubled the lead near the half-hour mark.
Spurs reduced the deficit through Toby Alderweireld's header in the 45th minute but couldn't make the most of lots of possession in the second half.
Bayer Leverkusen failed to hold onto a 2-0 lead in the group's other game, letting CSKA Moscow come from behind and rescue a point in a 2-2 draw. All four goals were scored in the first half.
Leverkusen missed plenty of opportunities after racing to a two-goal lead in the space of 15 minutes with goals from Admir Mehmedi and Hakan Calhanoglu. The Russian champion responded with two goals in three minutes courtesy of Alan Dzagoev and Roman Eremenko.
Sporting showed it has the quality to get through the group phase with a spirited performance that stifled the defending champions.
But Zinedine Zidane's coaching skills made the difference, as his decision to bring in Morata and James Rodriguez paid off. Rodriguez provided the assist, curling a perfect ball for Morata's header.
"It's a coach's job to make substitutions and we're happy that they paid off," Zidane said. "You make substitutions in order to change the game and that's what happened today. This is Real Madrid and we know we can always turn things around in a minute. We played a little better after conceding and we finally did it."
Sporting had the match at the Santiago Bernabeu Stadium largely under control and was rewarded when Brazilian midfielder Bruno Cesar gave scored with a shot from inside the area in the 48th minute. Ronaldo equalized from an 89th minute free kick.
Borussia Dortmund, the 1997 champion, enjoyed a stroll in the park at Polish champion Legia Warsaw, scoring with six different players in a 6-0 rout.
Riyad Mahrez scored twice as Leicester opened its maiden Champions League campaign with a comfortable 3-0 victory at Belgian champion Club Brugge.
Sixteen years after its last European game, the English Premier League champion was unfazed by the occasion and got off to a strong start, with Marc Albrighton scoring after just five minutes.
Mahrez then curled a free kick home and scored his second goal from the penalty spot.
The victory gave Leicester the lead in its group after FC Porto and Copenhagen drew 1-1.
Playing with a depleted side, Lyon relied on its homegrown players and the class of teenager Maxwel Cornet to open its Champions League campaign in style with a 3-0 defeat of Dinamo Zagreb.
Lacking five regular starters, including striker Alexandre Lacazette, Lyon dominated with a fine display of one-touch football. It quickly opened the scoring courtesy of Corentin Tolisso's goal.
Jordan Ferri, who honed his skills at Lyon's renowned academy with Tolisso, made it 2-0 four minutes into the second half from Cornet's assist. The 19-year-old Cornet then turned from supplier to scorer after playing a slick one-two with Tolisso.
Dinamo players were unlucky in the closing stages of the game, hitting the bar twice.
Lyon tops the group after Juventus was held to a disappointing 0-0 draw by Europa League winner Sevilla in their opening match.
Sergio Aguero kept up his explosive start to the season by scoring a hat trick for Manchester City in a 4-0 win over Borussia Moenchengladbach in their rescheduled Champions League match.
A 24-hour delay, after the original Group C fixture was postponed because of torrential rain, didn't put City off its stride as coach Pep Guardiola earned his seventh straight victory to open his tenure at the English club.
Aguero has now scored nine goals in five games this season after tapping in the opening goal in the ninth minute, converting a penalty in the 28th and completing his hat trick by rounding the goalkeeper in a one-on-one chance in the 77th.
Aguero was replaced by Kelechi Iheanacho, who wrapped up the scoring in stoppage time with a powerful close-range strike.