Luis Suarez made a strong return from his four-month biting ban on Saturday, showing no signs of being rusty and providing the biggest threat Barcelona could offer in a 3-1 loss at Real Madrid.
Suarez set up Neymar's fourth-minute opener and provided the most constant danger up front for the visitors, while Lionel Messi was kept in check by Madrid's defense.
Still, Suarez said the loss spoiled his good showing.
"Obviously, after such a long time not playing you are relieved to be back," said Suarez. "But I take away a bittersweet feeling because of the result.
"I'm thrilled to play again and begin a new chapter. You always want to debut with a victory. I leave with the sensation that the team did all it could to win but it wasn't to be."
In his first competitive match since sinking his teeth into an opponent at the World Cup, Suarez gave Barcelona coach Luis Enrique more than he had asked for.
"(Suarez) played well," Luis Enrique said. "He showed more pace than I had expected. He is an important player who knows how we play because he has been working with us."
Luis Enrique put Suarez in the starting lineup hours after he completed his hefty ban from club competition for biting Italy defender Giorgio Chiellini at the World Cup in June.
The suspension was the third multi-game ban Suarez has received for biting, having also been punished while playing for former clubs Ajax and Liverpool.
His performance on Saturday offered flashes of why Barcelona was undeterred by his latest act of gross misconduct and spent 97 million euros (then $130 million) to sign him from Liverpool during the offseason.
The Uruguay forward won corner kicks, battled with Madrid defenders Sergio Ramos and Pepe, and combined well with his teammates despite being limited to training and one friendly with them. He had also played a friendly with Barcelona's B-team and two with Uruguay.
Suarez already appeared familiar with his new teammates as he crossed for Neymar to dribble along the front of the area before firing in the opener in the fourth minute.
He then almost helped double Barcelona's lead with a pinpoint cross from the right side that Messi couldn't poke past goalkeeper Iker Casillas. Luis Enrique said that the missed chance was the turning point in the match.
"Neymar and Messi are very good, but we know how tough these matches are," Suarez said. "In the coming games we will try to combine more."
Madrid leveled through Cristiano Ronaldo's 35th-minute penalty. Pepe scored from a corner kick in the 50th and Karim Benzema hit on the break in the 61st to deal Barcelona its first league loss of the season.
"We were still in control with it at 1-1 but we couldn't convert our chances," Suarez said. "Then they got their goal from a set piece that surprised us and killed the match off with their speed."
Suarez was taken off in the 69th, showing that he's still a bit short of full match fitness.
"I substituted him, because I thought the last half hour could be tough for him," Luis Enrique said.
Madrid pulled to within one point of Barcelona at the top of the Spanish standings.
Suarez is still banned from playing for Uruguay in the Copa America and some World Cup qualifiers next year.