Fernandez-Castano and Pagunsan were tied at the weather-plagued tournament at 14-under-par 199 for after 54 holes.
They teed off on the first playoff hole at the par-5 18th hole only to have play stopped because of lightning. After an hour delay, each played his second shot but play was again called because of lightning. They are to resume Monday morning.
The tournament had a nearly three-hour suspension of play Friday because of storms and a weather-related break of more than five hours Saturday that led organizers to cut the tournament to 54 holes.
Fernandez-Castano was up by three strokes going into Sunday's play. He pushed up that advantage with an eagle at the fourth hole but had a bogey at the fifth. He birdied the sixth hole and took a four-stroke lead into the last nine. However, he toured the back nine the 3-over for a third-round score of 1-over 72.
Pagunsan ended with a 4-under 67 Sunday. He opened with a birdie and had two more at Nos. 4 and 7. His lone bogey of the round came at the eighth hole. He had a birdie at 15 and pulled into a tie with Fernandez-Castano with a birdie at 18.
Anthony Kim fired a 7-under 64 and Louis Oosthuizen a 65 Sunday and finished tied for third at 13-under. Joost Luiten (67) ended with at 12-under, tied with second-round co-leader Edoardo Molinari (71) and Danny Lee (68). James Morrison, the other co-leader, shot 1-over 72 in the third round and finished alone in eighth.
Swim Week Miami Beach 2014 [PHOTOS]