the unseeded dolgopolov - ranked 65th in the world , 64 places behind djokovic - surprised the serbian by winning a first-set tie-break and building a quick 4-2 lead in the second set .
djokovic steeled himself and rallied to force a decider , which he wrapped up without much resistance from his deflated ukrainian opponent .
novak djokovic came back from a set down to reach the quarter-finals of the miami open .