Barcelona's difficult first season without Lionel Messi has continued with a 2-1 home defeat in El Clasico to arch-rivals Real Madrid.
David Alaba's stunner and Lucas Vazquez's late tap-in enabled Carlo Ancelotti's team to beat their hosts at the Camp Nou.
The defeat was another blow to Barcelona - who are ninth, five points adrift of second-placed Real.
This was the first clasico without Messi, who scored 26 times in the famed fixture, and Madrid's long-time captain Sergio Ramos, former rivals who are now teammates at Paris Saint-Germain.
Messi was inevitably missed and this was illustrated when American full-back Sergino Dest, who had been shunted into the right flank position, squandered a golden chance prior to Clasico debutant Alaba arrowing in a brilliant shot.
Vazquez doubled the lead when he was on hand to tap in at the end of a second-half injury-time counter.
That proved crucial, with Sergio Aguero's maiden Barca goal deep in stoppage time coming too late.
The defeat was Barca's fourth consecutive Clasico defeat across all competitions - their longest losing run in the fixture since seven losses in a row between April 1962 and February 1965.
"Of course, it's an amazing feeling," Alaba said.
"My first El Clasico, my first goal. I'm very glad and grateful.
"But what's more important is the victory as a team, we're very happy to achive our goal."
Barca seemed all set to take the lead after breaking clear from a Marc-Andre ter Stegen pass only for Dest, with only Thibaut Courtois to beat, lashing a close-range effort way over the bar.
To compound the miss Alaba thumped home a wonderful finish into the top-right corner moments later.
"We had a very clear chance for the 1-0, and instead of that they scored the 0-1... It was such a clear chance. You have to put it in," Koeman said.
After the game, footage posted on social media appeared to show Koeman's car being surrounded by fans as he drove away from the stadium.
In response Barcelona posted a statement on their official Twitter account which read: "Barcelona publicly condemn the violent and disdainful acts that our manager experienced when leaving the Nou Camp.
"The club will take security and disciplinary measures so that such unfortunate events do not happen again."
Luis Suarez scored a second half brace as champions Atletico Madrid came from two goals down to draw 2-2 at home against leaders Real Sociedad.
Swedish striker Alexander Isak set up Alexander Sorloth in the seventh minute before he netted himself three minutes after halftime.
Suarez headed home around the hour mark before the Uruguayan completed the comeback when he was fouled in the area 13 minutes from time and converted the resultant penalty.
In other matches, Sevilla beat Levante 5-3, to remain level on points with second-placed Real, while fourth-placed Real Betis defeated Rayo Vallecano 3-2.
Australian Associated Press