Real, the record 10-times winners and 2014 champions, crushed 10-man Shakhtar Donetsk 4-0 at the Bernabeu, Atletico won 2-0 at Galatasaray and Europa League holders Sevilla thumped Borussia Moenchengladbach 3-0 at the Sanchez Pizjuan.
Champions Barcelona and Valencia, back in the continent's elite club competition after a two-year absence, can make it five wins out of five for La Liga sides when they play at AS Roma and host Zenit St Petersburg respectively later on Wednesday.
The success of Spanish clubs marked a sharp contrast with their rivals from the English Premier League, with Manchester United and Manchester City both surrendering their lead in 2-1 defeats at PSV Eindhoven and at home to Juventus.
Real forward Cristiano Ronaldo became the first player to reach 80 Champions League goals when he netted a Group A hat-trick against Shakhtar, who had midfielder Taras Stepanenko sent off five minutes into the second half.
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Portugal captain Ronaldo, who hit five past Espanyol in La Liga on Saturday, moved three clear of Barca forward Lionel Messi on the all-time scoring chart.
Afterwards, the 30-year-old hit back at critics who had suggested he might be past it after he failed to score in Real's opening two La Liga games of the campaign.
"Before I was bad and now I am good because I score eight goals," Ronaldo told Spanish television.
Antoine Griezmann struck twice for Atletico, the 2014 runners-up, as Diego Simeone's side made light of what can be a intimidating trip to Galatasaray's stadium in Istanbul.
The France forward said the Group C victory would help the team put Saturday's 2-1 La Liga defeat at home to Barca behind them.
"We knew the importance of starting the group phase with a win," he told reporters.
Sevilla coach Unai Emery said his side's Group D performance against Gladbach, when they missed one penalty but scored from two others, would help boost confidence as the Andalusians try to get their stuttering La Liga campaign going following a defeat and two draws in their opening three matches.
"Today we found the identity we are looking for this season," Emery told a news conference. "It gives us confidence to help turn around our results in La Liga."
(Editing by Sudipto Ganguly)
