Miami - Novak Djokovic remains on course for a record seventh Miami Open title, but the world number one was made to fight all the way to the last 16 in a 7-5, 4-6, 6-1 victory over spirited Federico Delbonis.
Djokovic is hoping to eclipse Andre Agassi's six ATP crowns in South Florida over the next week and although the 31-year-old endured some shaky moments at Hard Rock Stadium, he still possessed enough quality during the key moments to see off the battling Delbonis.
The Serbian wasn't happy with letting a 5-2 advantage slip in the first set and became furious with himself as the second squirmed from his grasp.
He will need to tighten up his game if he is to reach next Sunday's final with Roberto Bautista Agut waiting in the fourth round after the Spaniard defeated Italian Fabio Fognini 6-4, 6-4.
"Federico is playing well and it was really close at the start of the third set," said Djokovic who smashed 36 winners compared to 24 from Delbonis - whose excellent performance was punctuated with five double faults and a 67% success rate on his first serve.
"It was an exciting match and I am just pleased that I managed to hold my nerve," Djokovic said. "I got down on myself and Federico started swinging."
Djokovic had looked impressive in the second round win over Bernard Tomic and the Serbian continued his decent form by immediately imposing himself onto the Argentine.
The world number 83 struggled to contain Djokovic who was serving superbly and an early break saw the 15 time Grand Slam winner gain control.
Djokovic moved 5-2 ahead but after he missed a set point opportunity on the Delbonis serve, his game deserted him and suddenly, the South American had a spring in his step.
Delbonis had opportunities to steal ahead, yet calling on all his experience and mental resolve, the Serbian was able to hold firm and take the opener.
Delbonis continued to be competitive and brilliantly hit back after being broken for 3-1 which saw Djokovic hurl his racquet to the ground in utter frustration and receive a warning from the umpire.
The Argentine was hitting the ball superbly, especially from the back of the court, and another brilliant winner handed him two break opportunities which were taken when Djokovic sprayed long.
The world number one was getting incredibly frustrated yet credit to Delbonis who stayed calm and served out confidently to force a decider, something which looked beyond him midway through the opening set.
He couldn't keep the pressure on, however, and when Djokovic managed to get 3-1 ahead, this time there was no way back for the 28-year-old from Azul who rightly received an ovation from the center court crowd for his monumental efforts.
Results on Sunday in the Miami Open WTA and ATP Masters hardcourt tournament (x-denotes seeded player):
Novak Djokovic (SRB x1) bt Federico Delbonis (ARG) 7-5, 4-6, 6-1
Roberto Bautista Agut (ESP x22) bt Fabio Fognini (ITA x15) 6-4, 6-4
Kyle Edmund (GBR x19) bt Milos Raonic (CAN x12) 6-4, 6-4
John Isner (USA x7) bt Albert Ramos (ESP) 7-5, 7-6 (8/6)
Felix Auger-Aliassime (CAN) bt Hubert Hurkacz (POL) 7-6 (7/5), 6-4
Nikoloz Basilashvili (GEO x17) bt Robin Haase (NED) 7-6 (7/3), 6-3
Borna Coric (CRO/N.11) bat Jeremy Chardy (FRA) 6-7 (2/7), 6-2, 6-3
Nick Kyrgios (AUS/N.27) bat Dusan Lajovic (SRB) 6-3, 6-1
Karolina Pliskova (CZE x5) bt Alize Cornet (FRA) 6-7 (3/7), 6-1, 6-4
Yulia Putintseva (KAZ) bt Anastasija Sevastova (LAT x11) 1-6, 6-2, 6-3
Marketa Vondrousova (CZE) bt Elise Mertens (BEL x16) 6-4, 7-6 (7/1)
Tatjana Maria (GER) bt Sloane Stephens (USA x4) 6-3, 6-2
Wang Yafan (CHN) bt Danielle Collins (USA x25) 7-5, 6-1
Wang Qiang (CHN x18) bt Serena Williams (USA x10) walkover
Venus Williams (USA) bt Darya Kasatkina (RUS x14) 6-3, 6-1
Simona Halep (ROM x2) bt Polona Hercog (SLO) 5-7, 7-6 (7/1), 6-2