Inigo Martinez headed Athletic into the lead early in the second half but Memphis fired into the roof of the net in the 75th minute to earn Barca a point at San Mames.
Barca defender Eric Garcia was sent off late on for hauling down Nico Williams as the Athletic forward raced through, but it came too late for the home side to take advantage of their numerical advantage.
Barca earned a point when perhaps they deserved none. However, the sheer quality and resilience of Frenkie de Jong was brilliant, and Memphis pulled them through in the end.
De Jong was a driving force throughout, in attack and defence, while Memphis drifted in and out of the game but was the only player who looked capable of something special in the final third.
Aside from De Jong and Memphis, there were few positives. Martin Braithwaite missed a sitter early on before Athletic laid siege on Barca's goal, with Neto nervy every time he got on the ball. Oihan Sancet hit the bar in a first half dominated by Athletic, with Inaki Williams missing a string of chances.
Ronald Araujo, who had a goal ruled out for a Braithwaite foul on the stroke of half-time, later cleared off the line on an otherwise tough night for Barca's defenders. Pique went off injured after half an hour, and Garcia was turned inside out by the Williams brothers before being sent off.
Manager rating out of 10
5 -- Koeman didn't set his side up well for the challenge posed by Athletic. They were incapable of playing out from the back through the home side's press and the Dutch coach did little to change the tide of the game.
Player ratings (1-10; 10 = best, players introduced after 70 minutes get no rating)
GK Neto, 5 -- Not at fault for the goal but the Brazilian keeper struggled with his feet, putting his side under pressure several times.
DF Sergino Dest, 6 -- The American defender had some nice moments in attack, including one mazy run, but left too much space defensively.
DF Gerard Pique, 6 -- Pique had been advised to take a rest by the club's medical team before the game, so it was no surprise to see him limp off after 30 minutes.
DF Eric Garcia, 3 -- Was run ragged all night, with Athletic targeting him with Inaki Williams' pace. You almost felt for him when he was sent off late on for fouling Williams' brother, Nico.
MF Sergio Busquets, 6 -- Did ok on the ball, but due to a lack of support, was unable to help Barca bring the ball out from the back to kill the Athletic pressure.
MF Frenkie de Jong, 8 -- Brilliant throughout, covering every blade of grass. He made key contributions in defence, blocking an almost certain Williams goal, and was also involved in attack, hitting the bar and setting up a late chance for Memphis.
MF Pedri, 6 -- Was good for the first 45 minutes, tidy on the ball and carrying it forward when necessary. Tired after the break and came off on the hour.
FW Antoine Griezmann, 5 -- The Frenchman will have to produce much more in attack to help Barca in the post-Messi era.
FW Memphis Depay, 7 -- Not always brilliant but delivered big moments. Set up Braithwaite's early chance and scored the leveller with a great finish. Could have won the game late on but dragged wide.
FW Martin Braithwaite, 5 -- Missed a really good chance to open the scoring in the opening 10 minutes, blazing over from six yards.
DF Ronald Araujo, 6 -- The Uruguayan's pace and physicality was much needed alongside Garcia.
MF Sergi Roberto, 6 -- Came on to supply the assist for Memphis' goal.
FW Yusuf Demir, NR -- The Austrian came on to make his competitive debut for Barcelona at the age of 18.
DF Emerson Royal, NR -- A late introduction in place of Dest.