Ollie Watkins’ 73rd-minute goal earned the visitors their three points.
The winger took on Colwill in a run. The defender blocked the first shot but didn’t get another chance as Watkins buried the ball into the left post.
Earlier, former Barcelona left back, Lucas Digne, almost got the better side of Chelsea’s goalkeeper, Sanchez, after he whipped a shot before the keeper turned the ball over the bar.
Chelsea striker, Jackson, had a good chance a t goal but his weak left-footed strike was saved by Martinez.
Sanchez was called to action once more in the 39th minute after again saving the ball behind the bar from a volley struck by Nicolo Zaniolo.
Just before half-time, Chelsea’s Alex Disasi got his header into the back of the net before it was ruled offside.
Two minutes into the second half, Raheem Sterling was left through on a sublime pass from Thiago Silva.
The Englishman couldn’t convert his chance as Martinez came to the rescue of the visitors.
Chelsea’s woes continued late in the second half.
They were left to 10 men after French right back, Malo Gusto received his marching orders having received his second yellow
He made a late challenge on Digne before the referee sent him off the field.
The Blues continue to struggle to find their best form in the new season with five points in the opening six matches.
The Blues last played a 1-1 draw against Bournemouth after losing to Nottingham Forest on home soil.
