Two minutes from the end, Socceroo striker Scott McDonald had a chance to claim the game but he missed a sitter when he headed past the post from barely six yards out - and there was still time left for Boruc to save a Sandaza shot at his near post.

It contined McDonald's goal-free misery which has dates back to last season, with the pint-sized Aussie missing the traget throughout pre-season and beyond.

Paul Hartley's deflected goal six minutes after the break - and a controversial decision by referee Charlie Richmond to deny United a penalty when Roy O'Donovan clashed with Gary Caldwell - had looked likely to give the champions all three points.

But in the 79th minute the Spaniard, on as a second-half substitute for Warren Feeney, nipped in at the near post to flick a Craig Conway cross past Hoops goalkeeper Artur Boruc.

United were well worth their point and might have grabbed all three in the closing stages as they went all out for the winner.

However, they will point to the game's most controversial incident in which Richmond refused to award a spot-kick when O'Donovan appeared to be tripped by Celtic defender Caldwell inside the penalty area.

Richmond ignored the claims to the distress of the Tannadice supporters, then almost immediately injured himself by running in to Celtic midfielder Shunsuke Nakamura - and minutes later was substituted by fourth official Iain Brines.

The referee may have been spared by United's equaliser, which came in a second half in stark contrast to a dull first period.

United were first to threaten in the 10th minute when midfielder David Robertson climbed to head a Michael Kovacevic cross goalwards, Boruc stretching to tip the ball over for a corner - which the visitors survived.

Eight minutes later, O'Donovan incensed the travelling support when he was booked for barging Boruc as the Poland international shepherded the ball out of play. Tannadice left-back Danny Grainger then drove a volley from 16 yards just over the bar as the Taysiders had a spell on top.

Celtic threatened, with right-back Andreas Hinkel forging his way into the United penalty area - but goalkeeper Lukasz Zaluska was equal to the German's cut-back.

Just after the half-hour, Celtic midfielder Aiden McGeady picked up a yellow card for a foul on Kovacevic as the United defender drove purposefully down the right-hand side.

The champions looked increasingly dangerous - although Jan Vennegoor of Hesselink's close-range header from a Mark Wilson cross sped harmlessly over the bar.

Then, with five minutes of the half remaining, McGeady's stinging shot from the edge of the box had Zaluska scrambling to push the ball past the post for corner.

An in-swinging Hartley free-kick three minutes after the restart appeared to come off an arm inside the packed United penalty area and drew screams for a penalty from the Celtic fans - but Richmond was unimpressed and waved play on.

However, in the 51st minute the Hoops fans had something to cheer about when Hartley drove the visitors into the lead - albeit with the help of a deflection .

Nakamura had time on the ball inside the United box to lay the ball off to the former Hearts midfielder, whose side-footed shot came off Garry Kenneth before nestling in the corner of the net.

In the 55th minute, United were denied what seemed a clear-cut penalty when Caldwell seemed to trip O'Donovan inside the penalty area - close to the bye-line after the Irishman had turned inside the Celtic defender.

Richmond looked long and hard before ignoring a vigorous claim, then a minute later compounded what looked like one crucial mistake by running into Nakamura in the centre circle - leaving both men injured.

Richmond was substituted by Brines, and when the action resumed Zaluska did well to hold on to a fine long-range volley from Nakamura before Feeney's volley from 14 yards was safely held by Boruc.

In the 65th minute Vennegoor of Hesselink should have doubled the Parkhead side's lead when he was left with only Zaluska to beat from 12 yards out - but he drove his shot against the legs of the United goalkeeper.

United built up a head of steam and finally got the equaliser when Sandaza nipped in at the near post to direct a cross from Conway, himself on just seconds earlier for Willo Flood, past the helpless Boruc and into the far corner of the net.