In a marathon contest lasting four hours and 40 minutes, Nadal, winner of the event in 2009, fell to a surprise 7-6, 4-6, 3-6, 7-6, 6-2 loss against the world number 45.

Verdasco, beaten by his fellow Spaniard in the semi-finals seven years ago, produced an outstanding display in the deciding set, continually hitting the lines with a range of powerful backstrokes for which Nadal had no answer.

The result marked a poor start to the year for Nadal, who endured a difficult 2015 plagued by injuries, and marks the first time he has departed the Australian Open in the first round.

“I played unbelievably in the fifth set,” 32-year-old Verdasco, who will take on Israel’s Dudi Sela in round two, said.

“I don't know how I did it.

“I closed my eyes and everything went in.”

Nadal’s defeat came on a dramatic day at the event, the first Grand Slam of the year, during which women’s second seed Simona Halep was also on the wrong side of a shock exit as she was beaten in straight sets by Chinese qualifier Zhang Shuai.

Zhang, ranked at 133 in the world, earned her first-ever victory at a Grand Slam as she proved too strong for the Romanian, emerging with a 6-3, 6-4 success.

“I'm really disappointed,” Halep said.

“But it's only one day, only one match.

“She played without fear and she hit every ball.”

Elsewhere in the women’s draw, Britain’s Johanna Konta earned a memorable 6-4, 6-2 win over eighth seed Venus Williams, a nine-time Grand Slam winner, of the United States.

Wimbledon runner-up Garbine Muguruza of Spain is also through as she breezed to a commanding 6-4, 6-0 victory in her clash with Estonia’s Anett Kontaveit in exactly an hour.

In the men’s event, Australian Lleyton Hewitt prolonged his stay in professional tennis by overcoming fellow wildcard entry and compatriot James Duckworth 7-6, 6-2 6-4.

Hewitt, winner of two Grand Slam singles titles, is competing in his last Australian Open and delighted the crowd in Melbourne by progressing to the second round.

In another epic encounter, Frenchman Jeremy Chardy booked his place in the next phase thanks to winning the final set of his match with Latvia's Ernests Gulbis 13-11.

Olympic champion Andy Murray, the second seed and a four-time Australian Open runner up, cruised through in straight sets against Germany's Alexander Zverev, 6-1, 6-2, 6-3.