Sebastian Coates scored an unfortunate second-half own goal to gift Barcelona a 1-0 victory away to Sporting Lisbon in the Champions League on Wednesday.
The Uruguayan centre-back unwittingly deflected a Lionel Messi free-kick into his own net on 49 minutes to hand the Spaniards a second successive win to start Group D.
The five-time European champions head the section with a maximum six points, ahead of both Sporting and Juventus on three, with Olympiakos yet to pick up a point.
Ernesto Valverde's Barca have proved unstoppable in La Liga so far, winning their opening six matches to pull seven points clear of defending champions Real Madrid while vanquishing Juve in their first group game in Europe.
"We knew that to win we would have to suffer," Valverde told BeIN Sports Spain.
"We started strongly and dominated the first-half. After the goal we had 10 or 15 minutes where they pressed us and created some chances.
"But the Champions League is like this, you have to suffer to win."
Messi drew level with former long-serving Barca captain Carles Puyol by making his 593rd appearance for the club -- trailing only Andres Iniesta (638) and Xavi (767).
But the Argentine, one goal away from 100 in European competition, was largely subdued during a quiet first half in the Portuguese capital, with Cristiano Piccini flashing narrowly over for Sporting on 15 minutes.
Sergi Roberto slipped in Luis Suarez as Barca finally threatened just before the half hour, but the Uruguayan was denied by Rui Patricio with the Portugal goalkeeper then holding well from a Messi header.
Sporting's Marco Acuna tested Marc-Andre ter Stegen with a low drive, but Messi gradually grew in influence as the interval approached.
He weaved his way through the home defence on 43 minutes only to find an old foe, ex-Real Madrid full-back Fabio Coentrao, slide across superbly to block his goal-bound effort.
Sporting lost striker Seydou Doumbia to injury prior to the break, the Ivorian seemingly hurting himself following a theatrical fall on the edge of the Barca penalty area that earned him a yellow card.
Dutch international Bas Dost, who scored a league-best 34 goals last campaign, replace Doumbia, but Barca broke the deadlock early into the second half as a Messi set-piece ricocheted about the Sporting six-yard box before trickling beyond Patricio.
The Argentine's curling delivery in from the right brushed two Sporting heads with Suarez then nodding the ball against Coates who could only watch in horror as it dribbled over the line.
Suarez unleashed a snapshot straight at Patricio as Barca searched for a second, but the visitors were grateful to Ter Stegen as the Germany international thwarted Bruno Fernandes' attempt for an equaliser.
Former Tottenham Hotspur midfielder Paulinho went close to notching his third goal in four games late on when Patricio repelled the Brazilian, but Barca stretched their unbeaten run against Portuguese clubs to 15 matches dating back to 1987.