Teenage defender Pau Cubarsi was sent off midway through the first half of the tight clash in Lisbon with the score goalless.

Raphinha drilled home after 61 minutes to give five-time winners Barcelona a slim advantage on Bruno Lage's side ahead of the second leg next Tuesday.

Barcelona have not won the competition since 2015 but are expected to go deep this season, after a draw which many consider favourable.

Hansi Flick insisted before the game there was no such thing as an "easy" tie and the coach was proven right on a tense evening in the Portuguese capital.

"I said to the (team) chapeau, I'm very proud," said the German coach after his team emerged with a victory.

"After the 22nd minute with 10 players it was not easy, and this is a big win."

Goalkeeper Wojciech Szczesny endured two high-profile mistakes against Benfica in the group stage in January but made amends with a string of saves as Barca were pinned back in the final half hour.

Szczesny made a smart save to deny Benfica's Kerem Akturkoglu after just a few seconds, and the opening stages were played in a way that indicated both sides were picking up where they left off in Barcelona's wild 5-4 win in Lisbon.

"The last time I don't think (Szczesny) left here very happy," said Barca midfielder Pedri.

"He saved a lot (tonight), one at the start where if they score you start the game on a bad footing -- between the sticks he's a big presence and it's great to have him."

Dani Olmo fired narrowly wide at the other end as Barca threatened, before Benfica goalkeeper Anatoliy Trubin produced a stunning triple save to keep the score level.

The Ukrainian first parried Dani Olmo's prodded effort, then made a brilliant reaction stop to thwart Robert Lewandowski converting from point-blank range and mopped up Lamine Yamal's attempt from the rebound.

- 'We knew how to defend' -

Barcelona were dealt a blow when 18-year-old centre-back Cubarsi was sent off after 22 minutes.

The Spaniard scythed down Benfica striker Vangelis Pavlidis, who scored a hat-trick in the group match, as he ran through on goal.

Szczesny saved Orkun Kokcu's drive from the free-kick, with Flick sacrificing Olmo for defender Ronald Araujo to steady the ship.

The Polish goalkeeper, brought out of retirement by Barcelona after Marc-Andre ter Stegen suffered a severe knee injury in September, also made a fine reaction save to keep out Akturkoglu's header before the break.

Szczesny made another good intervention to keep Pavlidis at bay early in the second half before Raphinha broke the deadlock.

On the right flank after Flick replaced Yamal early in the second half with Ferran Torres, Raphinha stole in to win the ball back high up and wallop a low, deflected effort home from distance.

It was his ninth goal in nine Champions League games, with the forward in the form of his career.

"We had to be focussed, we had in our heads that we could get a chance and if we did, we had to score," said Raphinha.

Barcelona defended frantically in the final stages as Benfica sought to level and Szczesny came to the fore.

The hosts thought they had won a penalty when Szczesny felled Andrea Belotti, but there was an offside in the build-up and Barcelona survived with their lead intact.

"Today we knew how to defend," added Pedri.

"Afer the red we knew exactly what to do, stay together at the back, defend as a block and take advantage of our chances with the players we have up front."

Pavlidis said the Catalans were lucky to escape.

"Barcelona were lucky and scored the goal, we didn't and it's a big disappointment," said the Greek striker.

"Maybe on another day we could have scored three goals... there is a second game and everything is still up for grabs."