Without the inform Raven August and Nico Zambrano, the Royals matched Coastal for most of the game but were denied a deserved point when former Green Island player Weston Bell scored a late winner.
Coastal started with confidence having the majority of possession with the Royals content to force errors and counter quickly.
Coastal broke through in the 16th minute when Apisai Rabuka was left unmarked and tapped home.
The Royals responded on 27 minutes when Hayden Aish played the ball to Cato Williams just inside his half.
He took on his defender, and played a lofted pass behind the Coastal defence for Will Turner to run on to and he calmly slotted past keeper Ellis Hare-Reid.
Turner nearly gave the Royals the lead minutes later, but was denied when his long-range effort hit the crossbar.
Early in the second half, Coastal were denied when the lively Alejandro Steinwascher burst into the box and his thunderous strike struck the upright.
Coastal’s squad depth made the difference in the final 10 minutes.
Coastal were then denied a goal by the offside flag, but would get the decisive goal in the 83rd minute, when Bell was put through into the box and he guided his shot narrowly past outstretched hand of Royals keeper Alex Boomer.
A fantastic effort from the young Royals saw them return home empty-handed, but the team are improving and show they can compete with the top teams in the league.
They will look to build from that performance for their next clash against Selwyn at Tahuna Park.
The win keeps Coastal Spirit in third place, two points behind leaders Cashmere Tech, who had a routine 3-0 victory over Nomads.
Christchurch United are in second, who despite being a man down after only 26 minutes when Daniel Meyn was sent off, triumphed 5-1 against Selwyn. Nelson Suburbs beat Ferrymead 4-2.
University of Canterbury notched their first Southern League win in fine fashion when they ran away 6-1 against FC Twenty11, who are winless after seven rounds.
