The world number 116 kept his nerve to win through 6-3 5-7 7-6 (8-6) in two hours and 23 minutes, setting up a quarter-final against Croatia's Ivo Karlovic, who beat Alex Bogomolov Jr 7-6 (13-11) 6-4.
Second seed Andreas Seppi is now the title favourite after coming through 7-5 6-2 against Holland's Igor Sjisling, breaking his opponent twice in each set on his way to a comfortable 67-minute win.
Brazilian fourth seed Thomaz Bellucci beat another Italian, Flavio Cipolla, 6-4 6-1, but seventh seed Carlos Berlocq of Argentina was upset 6-3 6-4 by Poland's world number 74 Jerzy Janowicz.
In women's second round action, top seed Sam Stosur avoided Dolgopolov's fate with a 7-6 (8-6) 7-5 win over Alize Cornet of France, and fourth seed Ana Ivanovic saw off Russian qualifier Valeria Solovieva 6-1 6-4.
Seventh seed Maria Kirilenko came through 7-5 6-4 against Yaroslava Shvedova of Kazakhstan, while Serbian qualifier Vesna Dolonc continued her progress with a 6-1 6-0 thrashing of Romania's Simona Halep.