Birmingham, who were desperate for a win to ease their problems, appeared to be heading to defeat when Lee Carsley lobbed he ball from the left to Ayegbeni Yakubu to head forward for Lescott who nodded home.
Everything appeared to be against Birmingham salvaging anything from the game, but they rallied strongly and staged a grandstand finish.
Carsley, who had been booked for a handling offence earlier in the second half, handled again just outside Everton's penalty area.
Zarate, who is obviously a very confident youngster, stepped up to take the resulting free-kick and hammered his effort past Tim Howard.
Howard had earlier made a spectacular save to keep out a shot on the volley from Radhi Jaidi as Birmingham applied strong pressure.
Everton weathered the storm until Zarate arrived on the scene.
It's little wonder that Birmingham manager Alex McLeish is so keen to retain the South American, but he could face some fierce competition.
Earlier, Birmingham had suffered a serious set-back when they lost the services of the industrious Seb Larsson with a leg injury.
The little winger blocked a strong clearance by Leighton Baines and had to be replaced by Cameron Jerome.
It was Jerome who went closest to giving Birmingham the lead late in the first half when he saw his header from McFadden's cross gently hit the post and bounce clear.
Everton, however, often appeared the most likely goalscorers and it was fortunate for Birmingham that Stephen Kelly, Jaidi and Liam Ridgewell were in such as dominant mood.
Ridgewell, on his return from suspension, very nearly marked the occasion with a bad mistake the first time he cleared the ball.
His clearance cannoned off Andy Johnson and went just wide of Birmingham's goal.
Birmingham settled down to play some attractive football based upon some strong defensive play from Jaidi and Ridgewell.
Everton played with a lot of confidence with Carsley in a holding zone. Yakuba improved in the second half and it was hardly a surprise that he played a role in Lescott's 78th minute goal.
But the Merseyside club were denied success by the impish Zarate and his superb shooting skill that earned Birmingham a potentially vital point.