In what is fast becoming a familiar sight in the Vuelta's rare flat forays, Degenkolb benefited from a superb lead-out from his Argos-Shimano train before powering to a commanding victory ahead of France's Nacer Bouhanni (FDJ-BigMat) and Italian Daniele Bennati (RadioShack) in the 190km stage from Ponteareas to Sanxenxo.
With a fourth win in the race, the 23-year-old German moved back to the top of the green jersey standings ahead of race leader Joaquim Rodriguez of Katusha. Rodriguez finished safely in the peloton to conserve his 53-second lead over Britain's Chris Froome (Team Sky) ahead of Wednesday's all-important individual time trial.
Degenkolb launched his sprint from far back after being jostled superbly into position by Dutch team-mate Koen de Kort. Having passed the Italian veteran Bennati, Degenkolb had enough in the tank to hold off a late charge from French national champion Nacer Bouhanni and take his ninth win of the season.
"The sprint was really hard and the final was really just fighting," an ecstatic Degenkolb told Eurosport before paying tribute to his Argos Shimano team.
"The stage itself was not that hard because we controlled the race all day. The team did a really good job. I say it every time but it's true - I must thanks the boys," he said.
After Monday's long, 910-kilometre transfer from Barcelona and Tuesday's much needed rest day, the Vuelta resumed on the north-west coast of Spain with what promised to be a straight-forward day in the saddle - with temperatures much cooler in the early 20s.
Two Spanish Pro Continental riders broke clear of the pack inside the opening kilometres: this year's most aggressive rider, Javier Aramendia (Caja Rural), being joined by last year's most active, the veteran Adrian Palomares (Andalucia), in what was a cute piece of cycling symmetry.
The escapees negotiated the only test of the day, the Cat.3 Alto de San Cosme, two minutes off the front of the peloton before carving out a maximum lead of six minutes and 42 seconds as they rode north alongside the picturesque Galician coastline.
But there was only one script for the conclusion of the stage, and Argos Shimano and Katusha combined well to reel in the break with 33km remaining.
The Orica GreenEdge team of veteran Australian sprinter Allan Davis then took up the pace on the front before Team Sky took over the baton inside the closing 15km.
A small group of riders - including the faltering defending champion Juan Jose Cobo (Movistar) - were blown off the back of the pack, although the expected crosswinds never materialised.
Despite Sky's effort, the British team were left empty handed once again in the final sprint, with Ben Swift only managing ninth place. Their focus will shift to Froome for Wednesday's 39.5km time trial.
Last year's surprise runner-up behind Cobo, Froome will be amongst the favourites for the victory in the undulating race against the clock - although he will face stiff competition from Spain's Alberto Contador (Saxo Bank) and German time trial world champion Tony Martin (Omega Pharma-QuickStep).
Race leader Rodriguez, not a renowned time triallist, is expected to lose the red jersey in Pontevedra. The Spaniard leads Froome by 53 seconds and Contador by one minute ahead of the only ITT of the Vuelta.