Ronald Koeman insisted Barcelona remain upbeat and optimistic in their pursuit of the LaLiga title, despite suffering Clasico pain at the hands of Real Madrid.

Barca left the Spanish capital emptyhanded after Karim Benzema and Toni Kroos guided defending champions Madrid to a 2-1 win on Saturday.

Oscar Mingueza set up a dramatic final half-hour with his second goal of the season for Barca, while Madrid midfielder Casemiro was sent off in the 90th minute.

But Madrid held on at a sodden Alfredo Di Stefano Stadium to seal a third consecutive win against Barca in all competitions for the first time since 1978 as they provisionally moved top of the table, with Atletico Madrid in action on Sunday.

Barca are third and a point off the pace, though they could fall four points adrift if Atletico beat Real Betis.

"Of course we're still upbeat and optimistic because we've produced a serious performance," Barca head coach Koeman told reporters. "We are fighting.

"We lost a match against a team who are fighting to win the league but there are nine matches and all the matches are important for the three best teams.

"It's difficult for all three of us. We will come back, we will fight until the last match."

Barca attempted 12 shots in total in the second half, three of those on target, and nearly snatched a point when Ilaix Moriba struck the crossbar in the 94th minute.

But, Koeman became the first Barcelona coach to lose his first two LaLiga games against Madrid since Joaquim Rife in 1980 (also the first two).

Koeman could not hide his frustration post-match, having felt his side should have had a penalty when substitute Martin Braithwaite went down in the box under pressure from Ferland Mendy.

The former Netherlands boss said: "I'm not the only person who's upset about the decision, or lack of decision.

"The players feel disappointed because of this decision by the referee to not give the penalty and there's players who have been playing for years for Barcelona, so I know. But once again not all decisions were right.

"You should ask the players but I would like to include myself. We know that we've played a good match football wise, the first part, the first half, ok, we were not up to our standards. Real Madrid defended very well in the first half.

"There's no [league] match next week and the title [Copa del Rey final against Athletic Bilbao] is at stake. We have a week to prepare for a difficult match so we'll carry on and we are strong."

Lionel Messi, meanwhile, failed to score in seven consecutive Clasicos in all competitions for the first time in his career.