The Cottagers appeared poised to finally lift themselves off the foot of the table on the back of Ashkan Dejagah's first-half strike at The Hawthorns.
But just four minutes from time, goalkeeper Stekelenburg fluffed a 10-yard shot from 75th-minute substitute Matej Vydra as it squirmed under his body before just crossing the line, resulting in a 1-1 draw.
"The players are disappointed because we were so close to claiming the three points," said Magath, whose side continue to prop up the table.
"But we showed a lot of fight, which is what I want from my teams, and I was very satisfied with the first half.
"In the second half we then made too many mistakes, so we go home with only one point.
"But as a team we were close together, we fought very well, we looked like a team.
"We started very well and we had chances, the same as West Brom, but the more time went on, the more we went back like in recent games.
"But I've seen enough to feel sure Fulham will stay up. I was sure before the game, and I'm sure after the game.
"We were close to a win and the next game we will win."
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