* Ajax stun Barca with first half brace to win 2-1
* Barcelona not yet sure of first place in group (Adds detail)
Nov 26 (Reuters) - Ajax Amsterdam kept themselves in contention for progress to the next round of the Champions League after becoming the first side to beat Barcelona this season with a 2-1 triumph in their Group H match on Tuesday.
Thulani Serero and Danny Hoesen scored to give Ajax a surprise halftime lead but straight after the break defender Joel Veltman was red carded for a tackle on Neymar and Xavi pulled a goal back from the penalty spot.
Injury-plagued Barcelona applied pressure in search of an equaliser but Ajax held out to thunderous applause from a capacity Amsterdam Arena.
Ajax stay third in the group, one point behind AC Milan, who they must now beat away on Dec. 11 if they are to advance.
Group leaders Barcelona, without the injured Lionel Messi, are two points clear and not yet sure of top place though they were already through to the knockout phase before Tuesday's game.
Serero ghosted in late for the first goal in the 19th minute, applying the decisive touch to a strong cross from the right from fullback Ricardo van Rhijn, who just five minutes earlier had made a goal-saving tackle on Neymar.
The South African international's first Champions League goal precipitated a period of sustained pressure from the young Dutch side, culminating in a second goal three minutes from halftime.
A poor clearance from Javier Mascherano saw Ajax set up a chance for Viktor Fischer, whose shot was parried by goalkeeper Jose Manuel Pinto, only for Hoesen to pick up the rebound, go round Carles Puyol and score with the help of a deflection off Gerard Pique.
But the comfortable cushion deflated just two minutes after the break when Van Rhijn's poor back pass set Neymar away and Veltman tripped him on the edge of the area, conceding a penalty and getting himself sent off.
Xavi converted the spot kick to send Ajax into defensive mode as they tigerishly held on for the valuable three points, keeping Neymar at bay and ensuring the Brazilian has yet to open his Champions League goalscoring account.
It was Barcelona's first defeat under new coach Gerardo Martino and ended hopes of a record-equalling longest unbeaten start to a season.
They last lost at home to Bayern Munich in last season's Champions league semi-final. (Reporting by Mark Gleeson; Editing by Rex Gowar)