Although animating much of the finale, Salvatore Puccio (Sky) finished second followed by Cummings' team-mate, Natnael Berhane.
Cummings' post-race comments showed the strength of Dimension Data's bond.
"I didn't look too happy after I won because I felt sorry for my room-mate Edvald Boasson Hagen. We were racing for him," he said.
Ironically, Cummings' role to nullify attacks for Boasson Hagen was how he found himself in a winning position.
"I was sitting at the back of the breakaway group, working like a policeman to make sure no one was going to ride away from us. But with 3km to go, it looked like I was given victory on a plate, so I took the opportunity and I’m very happy about that," he said.
"At Dimension Data, we don’t have a big leader for the overall classifications. We now have a sprinter with Mark Cavendish but in every other stage, I enjoy that (the team) helped me to (wins like the) Tour de France stage win last year," he said. 
An early break of four riders kicked off proceedings from Montalto di Castro which an Etixx-Quickstep and Astana led peloton reeled back in with 31 of 222 kilometres left to race.
Zdnek Stybar (Etixx-Quickstep) remains in the overall lead at Tirreno-Adriatico (ANSA/LUCA ZENNARO) Source: RCS Sport
The two short but steep climbs of the Trevi and Montefalco also remained. Fabian Cancellara (Trek-Segafredo) tore apart the peloton in the lead-up to the final climb of Montefalco. Just 40 riders at the front topped it with 15km to go, led by Puccio.
The likes of Peter Sagan (Tinkoff) and Puccio attacked the pack but with Boasson Hagen's protection on their minds, Cummings and Berhane shut the moves down. But Puccio succeeded at 6km to go and Matteo Montaguti (AG2R-La Mondiale) and Cummings followed. They were ultimately joined by Berhane, Jan Bakelants (AG2R) and Daniel Moreno (Movistar) but it was to be Cummings' day.
Sagan remains in the Maglia Rossa after his team rode strongly to keep him at the pointy end. But the reigning World Champion still ponders the lack of assistance he receives from the peloton.
"After I managed to remain with the GC contenders in the hard climb where I’ve seen Fabian Cancellara riding very strongly, I sprinted but not for the stage victory, unfortunately.
"Cycling is difficult to understand. When other riders see me in a group, they don’t want to take me to the finish line in a winning situation," Sagan said.
Stybar is still overall leader and will be until Monday's stage after Stage 5 to Monte san Vicino was cancelled by race officials due to treacherous weather conditions.
