The mystery punter, with the username "Messi better than cesc", posted their forecast at 1905 GMT on Tuesday - a full 40 minutes before the match started.
Djibril Cisse would score very late on.
They suggested the deadlock would be broken by Xabi Alonso with a 40-yard strike after 38 seconds.
In reality, Sami Hyypia opened the scoring with a header 17 seconds later.
The prediction that Birmingham would trail 2-0 inside 10 minutes was also correct, as was the claim that Cisse would score late on.
The user thought Cisse would out-run the Blues defence before slotting home.
In fact, Cisse's shot should have been saved by Maik Taylor, but the goalkeeper allowed the ball to squirm under his body.
Still, not a bad prediction, especially when you consider that "Messi better than cesc" only missed out on the time of the own goal by two minutes.
Oliver Tebily put the ball in his own net after 77 minutes - and not 79 minutes by Emile Heskey as he or she had suggested.
Had "Messi better than cesc" done their research better, they would have known that Heskey had an ankle injury and was not fit to play.
Nevertheless, the 7-0 prediction would have netted odds of 100-1 from bookmaker William Hill.
"Oddly enough, although we took a few bets of a fiver or less at 100/1 for the 7-0 result prior to kick-off, the biggest bets we took for the scoreline were placed during game via the internet," said Hill's spokesman Graham Sharpe.
"One customer from Manchester staked £25 at 66/1 when the score was 3-0, and won £1650, while another from Cleveland picked up a profit of £1320 after betting £20. Overall, we lost a five figure sum on the outcome."
It is not known whether "Messi better than cesc" placed a bet on their forecast - but it certainly got the boards talking.
"Heskey" wanted to know what his or her lottery numbers were, while others requested racing tips.
Some even dared to chide the user for failing to predict the scorers in their correct order.
For those interested, the sequence of goals is shown below:
38 secs: Alonso 40-yard strike
10 mins: Alonso again
22 mins: Crouch with a 40-yard header
46 mins: Reina scores from goal kick
77 mins: Carragher gets his first goal in three years
79 mins: Emile Heskey og
90 mins: Cisse out runs every Brum player to finish
55 secs: Hyypia nods in the opener
5 mins: Crouch heads in
38 mins: The England striker makes it two with neat finish
59 mins: Morientes scores three minutes after coming on
70 mins: Riise smashes in from outside the area
77 mins: Olivier Tebily og
89 mins: Cisse's goal completes the rout