Tour of Britain stage 4: Redcar › Duncombe Park, Helmsley, 149.5km. Vuelta a España stage 17: Aracena > Monasterio de Tentudía, 162.3km.
The British rider was a key part of an aggressive Grenadiers performance which was punctuated by attacking moves throughout the stage and saw Omar Fraile finish fourth on the day to move up to second overall.
The duo now sit just seven seconds behind Serrano with four stages remaining of the week-long race.
After Magnus Sheffield had made the early break before being reigned in, the race really enlivened in the closing 50 kilometres.
Uno X Team set a fierce pace in a reduced bunch to try and deter attacks, but Pidcock led a three-rider group off the front by attacking on Carlton Bank.
This trio led until the closing kilometres when they were reeled in, only for Pidcock and Fraile to escape again shortly after.
With bonus seconds available atop the Newgate Bank climb, the Grenadiers sprinted as part of a four man group, only to gap the chasing pack.
This quartet then stayed away to the finish, with Serrano edging Pidcock on the line to take the race lead.
With the breakaway taking an early march on the peloton, the stage victory and bonus seconds were taken out of the equation, with Rigoberto Uran taking the victory.
Rodriguez then weathered attacks coming in from the other GC contenders to maintain fourth overall with four stages remaining of his first Grand Tour.