Brentford were beaten 3-1 by LaLiga side Celta Vigo at a freezing Jersey Road on Tuesday lunchtime.
The Bees took the lead after just 27 seconds, as Sergi Canos played in Yoane Wissa, who tucked the ball home from close range.
But Celta captain Iago Aspas inspired the Spanish side's comeback, as he found the net from the edge of the box to equalise in the first half.
Jorgen Strand Larsen tapped home from inside the six-yard box to put the visitors ahead after half-time, before Aspas completed the scoring with a looping effort from 40 yards, making it 3-1 in west London.
The teams
Thomas Frank started with a 3-4-3 at Jersey Road, which saw Keane Lewis-Potter feature at wing-back.
The back three were Zanka, Ethan Pinnock and Ben Mee, with Mads Roerselv on the right.
Ryan Trevitt and Vitaly Janelt started the game in central midfield, with Yoane Wissa and Sergi Canos either side of captain Ivan Toney in attack.
Celta boss Carlos Carvahal played a fluid 3-5-2 formation, with former Liverpool striker Aspas leading the line and captaining the Spanish side.
Brentford: Winterbottom; Zanka (Crama 80), Pinnock, Mee; Roerslev (Adedokun 80), Janelt (Gilbert 65), Trevitt, Lewis-Potter; Canos (Yarmoliuk 65), Toney, Wissa (Olakigbe 80)
Celta Vigo: Marche; Mingueza (Barcia 83), Unai, Carlos (Oscar 46); Kevin, Tapia, Gabri (Luca 69), Cervi (Perez 69), Galan; Larsen (Paciencia 69), Aspas (Duran 83)
First half
Brentford were ahead after just 27 seconds, as Canos raced down the right and clipped the ball into Wissa, who neatly struck past the goalkeeper Marche.
The first 10 minutes were littered with chances, first Celta, as Aspas played a delightful ball into Cervi, who opted to cross to Larsen instead of shoot, and the striker's sliding effort was well kept out well by Winterbottom.
And then Brentford, who almost found a second through Toney, as he picked up the ball on the halfway line after a smart counter attack led by Canos, but the striker, who spotted the goalkeeper off his line, sent his effort from 40 yards out just wide.
Canos and Toney were involved again, as the Spaniard chipped the ball over to the Bees skipper, who beat a man inside the box and then took it around the keeper, but his effort hit the side netting.
Celta were level soon after that, as Aspas received the ball on the edge of the box, before curling into the bottom corner of the Bees net.
The former Spanish international was involved again, as he and Oscar Mingueza combined well around the box, before Aspas’ shot from a similar area to where he scored his goal was held well by Winterbottom.
There was more pressure from the Spanish side just before half-time, as left-back Javi Galan received the ball on the touchline, before cutting inside well and playing the ball to Gabri, whose effort from the edge of the box went just wide.
Second half
Gabri played a part in Celta’s second, as he received a pass on the right side of the box, before sliding a clever ball into the 18-yard box to Larsen just two minutes into the second half.
The six-foot-four striker then had the simple job of tapping the ball in at the far post, putting Carvahal's side ahead.
Aspas made it three 10 minutes later after he, again, took a shot on from the edge of the box, which looped its way over Winterbottom and found its way into the Brentford goal from distance.
The Bees thought they had pulled one back on the hour mark when they had the ball in the net. Wissa poked home from close range after he challenged Marche, who dropped the ball, but the linesman already had his flag up to deny the striker.
The hosts pushed for a goal and couldn't have come much closer to one when Toney's acrobatic effort was only denied by a wonderful header from Renato Tapia, who prevented it from nestling into the top corner.
The Celta goalkeeper then did well to claim second-half substitute Alex Gilbert's cross, when there were plenty of red and white shirts waiting to pounce inside the area.
Frank's side had one more chance to reduce the deficit when the Bees won a free-kick on the edge of the box, but Toney's effort was saved well by the keeper.
Reaction - Keane Lewis-Potter
Keane Lewis-Potter said it was great to get 90 minutes and enjoyed playing in a slightly different role.