He placed his shot over a crowd of players and beyond Forest keeper Russell Hoult to give his side a share of the spoils.
Forest had taken the lead in the 54th minute when Willy Gueret pushed out a shot from David Johnson straight to Jack Lester who side-footed home.
There were two changes in the Swansea line-up with Leon Britton and Adebayo Akinfenwa coming in for Andy Robinson and Paul Connor, while Forest remained unchanged.
Britton had a fleeting chance in the ninth minute after Lee Trundle and Akinfenwa had worked an opening but Hoult came out smartly to gather.
Gary Monk was penalised for a challenge on Lester but Nicky Southall blazed well wide.
It was Southall who almost put his side ahead in the 15th minute when his shot took a slight deflection but Gueret stretched wide to save.
The Swans should have taken the lead in the 23rd minute when Trundle slipped a superb pass through to Akinfenwa. The giant striker raced towards goal but with only Hoult to beat he sent his shot well wide.
One minute before the break Sam Ricketts did well to block Lester when the former Sheffield United striker looked a certain scorer.
Forest took an undeserved lead when Lester was on hand to side-foot into an empty net after the home defence were slow to see the danger.
The goal lifted Forest who up until then looked a pale shadow of the side tipped as favourites for a swift return to the Championship.
Akinfenwa collected a Ricketts free-kick and moved in on goal before crashing a shot against the foot of the post with Hoult beaten.
Swansea continued to attack and a superb run and cross from Britton gave Akinfenwa a sight on goal but he sent his header high over the bar.
After the equaliser by Martinez, Swansea continued to look for the winner while Forest boss Gary Megson reverted to a defensive formation leaving only Johnson up front as he tried to hold on to the point.