Reina, whose horrible blunder gifted Argentina a goal in Spain's 4-1 midweek friendly defeat, produced a man-of-the-match performance in an otherwise forgettable display by Liverpool, who have won only one of their opening four league games.
Birmingham, unbeaten at home in the league for almost year and with two draws and a win to from their opening three games, were the more adventurous side throughout, buoyed by their good recent record against Liverpool.
The teams' previous six league meetings had been draws and though Liverpool chalked up a 7-0 FA Cup win at St Andrews in 2006 their last league victory over Birmingham came six years ago.
Reina made his first fine save after 25 minutes, diving low to keep out a Cameron Jerome header.
He reacted quickly to deny the same striker and produced a third terrific reaction stop to keep out Craig Gardner's point-blank header late in the first half.
Birmingham missed another good chance early in the second half when woeful marking left Scott Dann free but his header bounced just over the bar.
Liverpool, with striker Fernando Torres looking badly off the pace, were slightly better in the second period but still barely fashioned a decent chance and already lag seven points behind leaders Chelsea.
Chelsea made it four wins out of four on Saturday with a 3-1 success at West Ham United while Arsenal were also on form with a 4-1 home win over Bolton Wanderers.
Manchester United, who left out Wayne Rooney to spare him abuse from his former fans at Goodison Park, blew a 3-1 lead as Everton scored twice in stoppage time to snatch a 3-3 draw.
Former Liverpool manager Gerard Houllier returns to the Premier League on Monday when he takes charge of Aston Villa for the first time, away to Stoke City.
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