Baggies goalkeeper Scott Carson made some vital saves to keep his side in the contest and was rewarded when Jonas Olsson's shot rebounded kindly off the woodwork for Tamas to fire an 86th-minute equaliser to leave the visitors a point behind leaders Newcastle.
"We knew it was going to be difficult for us. A point here is a very good point and we had to chase the game for most of it," Di Matteo said.
"This was very exciting. We have had quite a few of those games where we battled away and got something out of it.
"Scott Carson was top drawer today. He kept us in the game. He was brave and everything you look for in a goalkeeper."
West Brom might even have had a penalty after the ball appeared to strike Matt Mills' hand, while Sigurdsson was lucky to stay on the pitch in the closing stages when he brought down Graham Dorrans in injury time.
"Some key decisions didn't go for us but my team never gave up and showed a real fighting spirit," Di Matteo added.
Speaking about the possible penalty against Mills, the Italian added: "It looked like a handball to us."
Reading boss Brian McDermott had seen his side win their previous six matches at the Madejski Stadium and admitted it was their inability to score a second goal that prevented them from continuing that run.
"We needed to get the second goal and we couldn't quite, but they are a class outfit and will be in the Premiership next season. They will be delighted to get a point," he said.
"I couldn't fault our players. They have given us everything again. We had just had three difficult games and could have had seven points, but got five.
"I don't see the point in talking about the play-offs. The only thing we can do now is see what happens against Ipswich.
"I don't need to talk to the players about the play offs to motivate them. I motivate them every game.
"Anybody who comes to the Madejski has got to do well to get anything. In 2010 we have not been beaten here in the league and we are really enjoying playing here."
McDermott denied that Sigurdsson, the Royals' leading goalscorer this term, should have seen red late on for his last-gasp challenge on Dorrans.
"I think there was a covering defender. I didn't see that as a sending off. They were baying for him to be sent off but that's all part of the game," he added.
"The players need a rest now. We will give them Monday and Wednesday off but we are really enjoying the games."