Colin Todd, the Bolton manager, said: "We keep moving up - we're up one place today - and it's still very interesting. Our effort is there but it's not being channelled in the right direction. We're that eager to get goals that we go right through the heart of a team and that makes it more difficult for us."
West Ham had already seen their own Wales forward John Hartson, up until then the visitors greatest threat, dismissed without hesitation by referee Paul Alcock in the 56th minute for apparently striking Bolton's Danish midfielder Per Frandsen on the back of the head.
Harry Redknapp, the West Ham manager, said: "I cannot defend John because, to me, it looked like he did it. We've lost John now for three games and that will be a big blow."
Bolton supporters sensed their first victory since the start of December as West Ham were reduced to 10 men but their thoughts came crashing down around them when Sinclair picked up Eyal Berkovitch's pass in the 65th minute to slot coolly past Keith Branagan.
Five minutes later Bolton should have equalised but were denied by a comedy of errors. Michael Johansen crossed but Alan Thompson miskicked completely from just five yards out and the clearly shocked Dean Holdsworth could only watch as the ball rolled past him.
Todd replaced the defender Chris Fairclough with Arnar Gunnlaugsson and it was the Icelandic substitute who came good four minutes from time when he crossed for Blake to head his 11th goal of the season powerfully past Craig Forrest.