It was one-way traffic from the first whistle in Catalonia, but an own goal from Dimitrios Nikolaou was all they had to show for their dominance before Pique was given his marching orders with three minutes left until the interval.
Second-half strikes from Lionel Messi – his 100th in European competition – and Lucas Digne were enough for Barcelona to maintain their 100% record in Group D, although a late consolation from Nikolaou did see Olympiacos breach the hosts’ defence for the first time in this season’s tournament.
Barcelona were quickly on the front foot as their visitors settled into an ultra-defensive formation which proved to be a theme of the match, but the hosts still created chances and should have been ahead inside five minutes when Luis Suarez failed to turn Samuel Umtiti’s flick on target at the back post.
The only blot on Barca’s copybook in the opening stages was Pique’s first yellow card for pulling back former Rotherham United and Norwich City loanee Vadis Odjidja-Ofoe, but it seemed like only a matter of time before they would make the breakthrough and Paulinho was the next to come close with a powerful long-range effort that fizzed over the crossbar.
Ernesto Valverde’s side were ahead moments later, though, as the lively Gerard Deulofeu volleyed a cross into the box which was sliced into his own net by 19-year-old defender Nikolaou.
Deulofeu continued to look the most likely to create something for Barcelona as Olympiacos packed all 11 players behind the ball, and the former Everton winger almost made it two in as many minutes when his low drive was kept out by Silvio Proto.
Proto found himself in no-man’s land midway through the half when Paulinho latched on to Andres Iniesta’s chipped pass forward, but Olympiacos were saved by the woodwork as the Brazilian’s header came back off the crossbar with the keeper beaten.
Sergio Busquets was the next to threaten as Barcelona continued to knock on the door, and the second goal should have arrived shortly after the half-hour mark when Messi slipped a pass through for Suarez, who was denied from inside the area with only the goalkeeper to beat.
The rain was pouring down in front of a sparse Camp Nou crowd, but the floodgates were not opening for Barcelona and Olympiacos finally had their first and only shot of the first half with less than 10 minutes remaining when Odjidja-Ofoe hooked an ambitious volley wide of the target.
Barcelona were back on the front foot seconds later, though, and Messi was forced to wait a little longer for his milestone goal when he was denied by Proto from inside the area.
An entirely dominant first half should have yielded more than one goal, but it ended on a low note as Pique was shown his second yellow card three minutes before the interval. The Spain defender thought he had doubled his side’s advantage when bundling the ball over the line from close range after Deulofeu’s low drive has been saved, but Scottish referee Willie Collum correctly ruled that he had used his hand to turn it home.
Deulofeu had been Barcelona’s star of the first half, but he was the unfortunate player to be sacrificed at the interval as Valverde brought on Javier Mascherano to cover for Pique’s red card.
Olympiacos looked to capitalise on their newfound glimmer of hope with a more adventurous mindset in the second half, but it was still Barcelona that created the bulk of the chances and Suarez fluffed his lines from a good position in the opening stages after the restart.
It was Messi who finally gave the home side a two-goal cushion, though, bringing up his century of European goals in style with a 25-yard free kick which Proto could not keep out despite getting a hand to it.
The Argentine had been quiet up until that point, but the goal sparked him into life and he was instrumental as Barcelona made it two goals in three minutes moments later, skipping past his marker before pulling the ball back for Digne to drill home.
With the pressure relieved courtesy of the quickfire double Barcelona rediscovered their swagger in the final 25 minutes and they would have had a fourth but for a brilliant double save from Proto, who denied first Paulinho and then Messi from point-blank range.
Messi and Paulinho both threatened again in the closing stages, but it was Olympiacos that got the last laugh when Nikolaou – who had earlier scored an own goal and conceded the free kick that Messi dispatched – went some way to redeeming himself by rising highest in the area to plant a header into the top corner.
It was not enough to change the result at Camp Nou, although a late goal elsewhere in Group D did have an impact as Juventus rescued a victory against Sporting Lisbon to ensure that Barcelona’s lead at the top of the standings remains at just three points.
Valverde’s side are now six clear of third place, though, and could seal a place in the last 16 for the 14th season in a row should results go their way when they meet Olympiacos again in a fortnight’s time.