MADRID (AP) — Cristiano Ronaldo hopes Real Madrid learned its lesson after almost losing at home to Sporting Lisbon in its Champions League opener.

Madrid's late comeback on Wednesday night gave the defending champions a winning start in the group stage, but the team's disappointing performance at Santiago Bernabeu Stadium raised some concerns.

Ronaldo grabbed an 89th-minute equalizer with a superb free kick, and substitute Alvaro Morata netted the winner with a powerful header four minutes into injury time for a 2-1 win over the Portuguese side with which Ronaldo started his career.

"This game serves as a warning that we can't be starting games so poorly," Ronaldo said. "Because teams will sweep the floor with us and we don't want that. We want to finish top of the group and win."

The Spanish powerhouse struggled throughout, failing to create significant scoring opportunities and unable to keep Sporting from threatening on counterattacks. Madrid entered the game heavily favored to win but it was Sporting which was mostly in control at the Bernabeu.

"We were a bit flat at the start, but such is football and such is Real Madrid, and the comebacks are part of this mythical stadium," said Ronaldo, who made his 350th appearance for Madrid.

The Portugal forward put his team back in the game by curling a right-footed shot over the leaping wall and into the top corner. Sporting goalkeeper Rui Patricio got his hand to the ball but it went off the post and across the line. Ronaldo didn't celebrate the goal against his former club, except for putting his hands in the air.

"It was against the team where I learned my trade, the club has a place in my heart," Ronaldo said of Sporting. "I have a lot of respect for them, that's why I couldn't celebrate it."

Madrid is trying to become the first team to win back-to-back Champions League titles in 26 years. After one game, it is tied with Borussia Dortmund atop Group F with three points, but trails on goal difference because Dortmund routed Legia Warsaw 6-0.

"We'll analyze the aspects that I didn't like," Madrid coach Zinedine Zidane said. "What I do know is that we can perform better than we did. We came up against a team that played their game and made it difficult for us. This is the Champions League and nothing is easy in football. There are no easy games."

The comeback came after Zidane made some key changes, adding substitutes Lucas Vazquez, Alvaro Morata, and James Rodriguez. The team improved significantly, with the winner being scored by Morata after a cross by Rodriguez. It was the first time this season Madrid played with the attacking trio of Ronaldo, Gareth Bale, and Karim Benzema in the starting lineup.

Zidane said the hard-fought victory should boost the team's confidence going forward.

"When you win a game in this manner it means a lot to the squad," Zidane said. "That's what I take away with me and I go home with a smile on my face and feeling very relaxed. We can't win all of our games 5-0. We had to dig in, but we got the three points."

Madrid's next Champions League game is at Dortmund on Sept. 27. It plays at Espanyol on Sunday in the Spanish league, a competition it leads with three wins from three rounds.