Northampton launched a multi-phase attack but just when it looked they had created men over down the right, Saints captain Dylan Hartley was hit in a man-and-ball tackle by 21-year-old England prospect Cato.
The keeper would have been powerless to deny Essien from close range after he was found by Branislav Ivanovic's cross in the third phase of the same attack, but the Ghanaian somehow poked wide.