This is Arsenal’s first Carabao Cup final since 2018.
Semenyo said, “First half we played really well. The mentality was to do the same again.”
The result meant that Arsenal will provisionally stay seven points clear of Manchester City in the title race.
The first leg of the playoff ties will be played on February 17 and 18 while the return legs will take place on February 25 and 26.
Anatoliy Trubin sealed the victory for Benfica as the goalkeeper headed home a free kick.
Despite the defeat, Arsenal retain top spot with a four point lead over second placed Manchester City.
The players are expected to reimburse the 374 fans £9,350.
Gabriel Jesus scored a brace as Arsenal defeated Inter Milan 3-1 on Tuesday, sealing qualification for the UEFA Champions League last 16 with a dominant display at the San Siro.
Arsenal edged towards their first League Cup final since 2018 as they beat Chelsea 3-2 in the opening leg of their semi-final at Stamford Bridge on Wednesday.
City controlled 67 per cent of the ball and registered 14 shots, yet could not breach a resolute Sunderland defence on a freezing New Year’s Day in the North East.
