Nadal, who finds himself in a star-studded bottom quarter of the draw with Novak Djokovic and Roger Federer, was hampered by illness earlier in the week and initially fell a break down on Monday (AEDT).

However, that early scare was swiftly overcome as the Spaniard - a three-time winner of this event - comfortably avoided the sort of upset that world number one Andy Murray suffered at the hands of Vasek Pospisil 24 hours earlier.

Pella may have started confidently, in his first meeting with Nadal, but the world number 145 was soon overwhelmed by his illustrious opponent's superior power on a sweltering day in California.

A sloppy smash from Pella was punished ruthlessly by a superb forehand winner as Nadal immediately recovered the break he had given up in game three, before enjoying further success in the Argentinian's next service game.

Nadal was in complete control by the time he served out the opener with an ace and then broke again at the start of set two

The fifth seed was guilty of a brief lapse in concentration, allowing Pella to break back, and the underdog's confidence was clearly lifted as he went on to play a couple of eye-catching strokes, including a reflex volley winner that drew gasps from the crowd.

Yet Nadal soon regained the initiative, breaking for a 3-2 lead at the end of the game that had featured Pella's good work at the net, and proceeded to book a third-round tie with either Fernando Verdasco or Pierre-Hugues Herbert.