Kshitij Naveed Kaul, 18, was the top amateur, while Sharma (4-under 284) won the Indian Golf Union prize for being the top Indian player.
Wallace entered the final day with a share of the lead and a closing 68 got him to 11 under, a total matched by compatriot Johnston after a 66.
Wallace hit a huge drive down the 18th on the first extra hole and with Johnston laying up and seeing his birdie putt agonisingly lip out, the 27 year old had two putts for the title after hitting a brilliant second onto the putting surface.
He rolled his first up to the side of the hole and tapped home to seal a second victory in 32 appearances after last season’s triumph at the Open de Portugal at Morgado Golf Resort.
American Sihwan Kim finished at eight under, a shot clear of Spaniard Pablo Larrazábal and Austrian Matthias Schwab.
Argentinian Emiliano Grillo was then five under, with home hero and Race to Dubai Rankings presented by Rolex leader Shubhankar Sharma and Scot Stephen Gallacher a shot further back.
Wallace was playing on the Alps Tour in 2016 but six wins that season – including five in a row – got him onto the Challenge Tour and he continues his meteoric rise following the victory in Portugal in just his fourth European Tour event.
Leading Scores:
277 – Matt WALLACE (ENG) 69-70-70-68, Andrew JOHNSTON (ENG) 72-66-73-66.
280 – Sihwan KIM (USA) 70-70-72-68.
281 – Pablo LARRAZABAL (ESP) 67-71-74-69, Matthias SCHWAB (AUT) 71-72-68-70.
283 – Emiliano GRILLO (ARG) 65-68-78-72.
284 – Stephen GALLACHER (SCO) 72-71-67-74, Shubhankar SHARMA (IND) 73-64-72-75.
286 – Jinho CHOI (KOR) 72-71-72-71, Joost LUITEN (NED) 71-69-74-72, Aaron RAI (ENG) 71-73-69-73.
287 – Robert ROCK (ENG) 73-73-74-67, Keith HORNE (RSA) 66-73-80-68, Clement SORDET (FRA) 72-72-71-72, Hideto TANIHARA (JPN) 74-68-72-73.
288 – James MORRISON (ENG) 70-72-77-69, Jens DANTORP (SWE) 69-70-79-70, Gavin GREEN (MAS) 69-73-75-71, Panuphol PITTAYARAT (THA) 69-70-76-73, Steven BROWN (ENG) 74-71-70-73, Ricardo GOUVEIA (POR) 69-73-71-75.
(Read more in the April issue of Golf Digest India. Download here.)