Andreas Seppi fought back from losing the opening set to gritty American qualifier Ryan Harrison to register a 3-6 7-5 6-3 win on Court 2.
The Italian ace, Eastbourne runner-up last year following his maiden ATP Tour title by wining the 2011 AEGON International, was expected to steamroll past Harrison.
But Seppi, the no7 seed, was given an early scare after being outplayed by the young gun firing formidable shots from all angles.
Harrison, having collected four victories in as many days, chased every point but midway through the decisive third set he was visibly tiring with his fantastic exploits at Devonshire Park finally taking their toil.
Another Italian seed, Fabio Fognini, also had to bounce back from losing the opening set before booking his quarter-final berth.
Slovakian Martin Klizan edged the tiebreak 8-6 before being outclassed by Fognini to lose 6-7 6-2 6-2 on Court 4.
Radek Stepanek turned up the heat to dispatch of big serving Philipp Kohlschreiber 7-5 6-3 and start the scattering of seeds on the hottest day in England so far this year.
The Czech veteran, who last year won just four matches on grass, swiftly found his feet to reel off the opening set in a tepid tie watched by a less than half full Court 1.
Kohlschreiber, the no3 seed, failed to recover from narrowly losing the first set and his stuttering display gifted the 34-year-old a quarter-final spot.