West Ham 1 Aston Villa 1: Argentina striker Carlos Tevez came off the bench for his West Ham debut as his new club fought back to earn a point against Aston Villa, for whom another new face, Stilian Petrov, impressed in the centre of midfield at Upton Park.
Liam Ridgewell's fourth-minute strike had earned Villa the lead and the Hammers were fortunate not to be further behind at half-time after two Juan Pablo Angel headers hit the crossbar.
West Ham had lacked their usual fizz and were indecisive at the back — but they burst into life after the interval and were level within six minutes when Bobby Zamora deflected Paul Konchesky's header past Thomas Sorensen for his fifth goal of the season.
These are exciting, if uncertain times at Upton Park with a potential takeover in the pipeline — which is understood to have prompted the departure of financial director Nick Igoe from the board — coupled with the mysterious manner in which Tevez and Mascherano arrived at the club.
In an address to the fans before kick-off, Alan Pardew vowed he would "protect the integrity and the traditions" of West Ham but urged supporters to embrace what is "perhaps the start of a new era".
Pardew could have dropped Hayden Mullins and Zamora to make way for the newcomers but he wanted to send a message that both remain an integral part of West Ham.
"These boys (Tevez and Mascherano) wouldn't be here without the likes of Bobby Zamora and Hayden Mullins," said Pardew.
The moment all West Ham supporters had been waiting for arrived after an hour when Tevez replaced Marlon Harewood.
There were immediate flashes of what West Ham and the Premiership can expect this season. At one stage Tevez left Martin Laursen for dead inside the Villa box.
He could not conjure up the winner — but after the way West Ham started, they will surely be grateful for a point.
They struggled to contain Villa at the back, especially in the air, and fell behind after just four minutes.
Roy Carroll produced a superb reaction save after Gabriel Agbonlahor had risen to meet Gareth Barry's in-swinging corner — but Ridgewell reacted quickest to pounce on the loose ball and put Villa ahead.
West Ham responded positively, Yossi Benayoun feeding a clever pass through to Zamora in the box, though the angle was too tight for a decent shot.
Sorensen then presented Harewood with a golden opportunity after scuffing a clearance straight to the Hammers striker, who poked it poorly wide.
West Ham were lucky to escape when Angel rose unchallenged to crash his header against the bar from another dangerous corner.
Luke Moore easily got the better of Tyrone Mears and the home side once again struggled to clear a corner as the ball bounced around the box six-yard box.
Villa caused further problems to the home defence when Barry curled in a deep cross, Angel beat Danny Gabbidon and glanced another header off the crossbar.
West Ham drew level within minutes of the restart. Bowyer's corner picked out Konchesky on the edge of the box and his powerful header bounced deflected in off Zamora's thigh.
The game had come alive. Petrov lobbed Carroll but Mears cleared his lines with a flying overheard clearance.
Barely a minute later, Anton Ferdinand hacked the ball off his own line after Carroll had produced another top-class save, this time to deny Barry's swerving strike.
With the momentum on West Ham's side, Pardew replaced Harewood with Tevez.
He was followed by Matthew Etherington and Carlton Cole but they could not create a winner.
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