London - Lionel Messi inspired a return to form for Barcelona in a thrilling 4-2 win at Tottenham Hotspur that leaves the English side with a mountain to climb to reach the last 16 of the Champions League.
Spurs have now lost their opening two games in Group B to fall six points behind Barca and Inter Milan and were left to rue a slow start.
Philippe Coutinho put the visitors ahead inside two minutes before Ivan Rakitic's spectacular volley doubled Barca's lead before half-time.
Harry Kane and Erik Lamela twice reduced Spurs' deficit, but Messi made the difference by scoring a double as the La Liga champions withstood a rousing finale from the hosts.
Messi means Champions League business
The Catalans' domination of domestic matters in La Liga in recent years has been overshadowed by eternal rivals Real Madrid's romp to three consecutive Champions League titles.
Barca set their stall out to end Real's European reign before a ball was even kicked this season with Messi in his first statement as new club captain after the exit of Andres Iniesta promising to "bring this beautiful cup back home to the Camp Nou".
On the site of two of Barca's greatest ever triumphs where they won the European Cup in 1992 and 2011, Ernesto Valverde's men dispelled any doubts caused by a three-game winless run in La Liga.
Draws with Girona and Athletic Bilbao either side of a shock defeat by Leganes were partly caused by Valverde prioritising the Champions League with Messi left on the bench at the weekend.
Back in the side, the five-time World Player of the Year ran the show, also hit the post twice as his two goals and brilliant first-half finishes by Coutinho and Rakitic earned all three points for the visitors.
Messi now has five goals in just two Champions League games this season.
Spurs squad exposed
Tottenham are already paying for the club's failure to add a single player in the transfer market to a squad burned out by World Cup commitments.
From the side that famously beat Real Madrid 3-1 at Wembley just under a year ago; Jan Vertonghen, Mousa Dembele, Christian Eriksen and Dele Alli were all absent through injury.
Beating Barca at full-strength is hard enough but Spurs simply don't have the squad depth to compete with the best when so many of their key men are missing.
That lack of investment threatens to stall Spurs' progress under Mauricio Pochettino as having reached the last 16 last season, an early Champions League beckons unless there is a big turnaround after starting with two defeats.
Oh no Hugo
The one injury boost for Spurs appeared to be the return of captain Hugo Lloris in goal for the first time in five weeks.
Lloris has endured a troubled time after admitting to drink driving during his absence with a thigh injury.
Another poor decision from the French World Cup winner gave his side a mountain to climb as he raced from his goal and got caught in no man's land when Jordi Alba teed up Coutinho for the opener.
Messi could have profited from another erratic Lloris moment, as the goalkeeper ran outside his box just as Spurs got back into the game at 3-2, before the Argentine's second goal settled matters late on.