Reading boss Brian McDermott thought they were through to the FA Cup quarter-finals before a dramatic late show from West Brom.
The Royals put themselves in the history books when they scored one of the fastest goals in the competition as Jimmy Kebe slotted home with just seven seconds on the clock.
Roberto Di Matteo's last minute selection of Robert Koren proved vital when the Slovenian equalised in the 18th minute.
However, following the dismissals of Reading's Shane Long and Baggies substitute Youssouf Mulumbu, McDermott was convinced his side would be through to the quarter-finals when Simon Church scored in the 73rd minute.
"I thought we'd won it," said the Reading boss.
"We changed the system when they went down to 10 men and we went for the win and when Simon scored I thought we were through."
However West Brom, who are currently second in the Championship race for promotion, forced a replay at The Hawthorns when full-back Joe Mattock netted a stunning strike with just three minutes to spare.
"Fair play to them, they are a quality side and it was a superb goal at the end to get the equaliser," said McDermott.
"I think West Brom will definitely be in the Premier League next season and they showed their quality.
"The goal so early on was incredible - we worked on that in training!
"But Jimmy has got so much pace that he can do that."
The 48th minute dismissal of Long means the forward will face a three-match ban which could prove costly in Reading's fight against league relegation.
However McDermott defended the Republic of Ireland international who was shown a straight red for lunging into a challenge with Abdoulaye Meite.
"Shane went for the ball and he was half a second late but he is an honest player and there was no malicious intent," he said.
"I'm not sure if it warranted a red card but it is up to the referee to make that decision.
"This is a great cup competition and to get into the last eight would be a hell of an achievement, and we still have every chance.
"There will be a big crowd at The Hawthorns I am sure and it is another good game to look forward to."