After his wife Natalie had given birth to a baby boy on Tuesday, the 29-year-old battled back from a toe injury that kept him out of England's recent Euro 2004 qualifiers to volley in a superb 22nd minute winner that lifted the Hammers off the bottom of the Premiership table for the first time since August.
It was a deserved victory that owed as much to the battling spirit of Glenn Roeder's team as it did to Sinclair's excellent goal. While many in the game expected Hammers to come unstuck against a freshly optimistic Sunderland side apparently rejunvenated by the arrival of Howard Wilkinson and Steve Cotterill, the visitors approached the task in the perfect fashion, defending solidly to frustrate the hosts and attacking on the break whenever possible.
Following the disappointing 2-1 defeat against Birmingham City a fortnight ago, Glenn Roeder made notable changes. Ian Pearce came in for only his third start of the season as part of a defensive reshuffle that saw Gary Breen drop to the substitutes' bench, while Christian Dailly returned to the starting line-up in the right-back position as a replacement for the injured Sebastien Schemmel.
After an understandably nervy start, with neither side willing to commit too many bodies forward, it was a bolt from the blue when Hammers opened the scoring with their first real attack of the game in the 22nd minute.
Collecting a throw-in from Scott Minto on the halfway-line, Di Canio turned infield and, spotting the run of Sinclair, sent a superb pass across field that dropped in behind Michael Gray and allowed the England midfielder to run clean through goal before firing a magnificent right-foot volley past Jurgen Macho that crashed in off the crossbar. Trevor and his team-mates of course celebrated with the customary 'rock the baby' celebration, as Wilkinson and Cotterill faced up to the teething problems now facing them.
The goal gave Hammers an immediate lift in confidence and allowed them to find their natural passing rhythm as the first half wore on, with the hosts restricted to just two half-chances from corners that fell to defender Jody Craddock.
In fact, it was the visitors who really should have extended their lead in the final 10 minutes of the half, with Joe Cole handed two decent opportunities. First he latched on to a Jermain Defoe pass and saw his goalbound shot excellently tipped round by Macho, then he capitalised on a slip from Phil Babb to skip into the penalty area, but took one touch too many and was crowded out before getting his shot in.
Two minutes before the break, Hammers suffered a blow when Pearce was forced to leave the field with a shoulder injury sustained in a run-of-the-mill aerial challenge. The big defender raised eyebrows by appearing for the second half and performed admirably to last another 22 minutes before the problem became unbearable and Gary Breen took his place
Predictably, the Black Cats displayed a renewed sense of determination after the interval, with pacy substitute David Bellion causing immediate danger on the right flank. Striker Kevin Phillips went close with a low shot in the 48th minute, and thought he had equalised four minutes later when he followed up Bellion's stinging shot that was only parried out by David James, but the linesman's raised flag rescued the Hammers.
After weathering that storm, the visitors began to find their feet again and regain some attacking force. Sinclair almost bettered his opener with a fantastic run from the halfway-line and shot that was blocked by Macho, while Di Canio saw a hooked effort saved well by the Sunderland keeper at his near post.
Perhaps the hosts knew it wasn't going to be their day in the 75th minute, when a cross from the right found it's way through to substitute Niall Quinn at the far post. The veteran Irishman teed the ball up before measuring a delicate volley that beat James and looked destined for the far corner of the net but rebounded off the post and was cleared by Lomas.
However, this result wasn't about luck. Even after match-winner Sinclair was forced to leave the field in a daze following a typically brave challenge late on, the determined Hammers stood firm in all areas of the field as Sunderland were reduced to lumping aimless balls into the danger area in search of an equaliser.
The final whistle brought delight to the hundreds of loyal travelling supporters that had made the trip north, and Roeder will be hoping for further triumph on Wednesday night when the Hammers face a slightly shorter journey to face high-flying Fulham at Loftus Road.