The Argentinian knocked out Japan's Shingo Kunieda, an eight-time former champion, at the Chikuho Heights Tennis Courts in Iizuka.

After the first set was taken to a tiebreak, Fernandez, the 2012 winner, wrapped up a 7-6, 6-4 success.

Kunieda, a triple Paralympic champion, exits the tournament while on the recovery trail from injury.

However, Japan still have interest in the men's draw after Takashi Sanada and Takuya Miki both advanced.

Sanada beat compatriot Daisuke Arai 6-1, 6-0 to set up a quarter-final clash with Fernandez.

Miki upset Sweden's world number six Stefan Olsson, a doubles Paralympic gold medallist from London 2012, 6-0, 6-4.

He will now play France's world number one Stephane Houdet, who ousted Abu Samah Borhan of Malaysia 6-1, 6-0.

Britain's Alfie Hewett won by the same score against Thailand's Banjob Suwan.

He will meet France's Nicolas Peifer, a 6-4, 6-2 winner over Thailand's Wittaya Peem-Mee.

Rio 2016 Paralympic gold medallist Gordon Reid of Britain knocked out 2002 Japan Open winner Satoshi Saida of the host nation, 6-2, 6-2. 

His reward is a tie with Dutchman Maikel Scheffers, the 2013 winner, who saw off Ha-Gel Lee of South Korea 4-6, 6-1, 6-3.

In the women's draw, Thailand's Sakhorn Khanthasit caused a shock by disposing of The Netherlands' world number four Marjolein Buis, 6-4, 6-1, to reach the last eight.

The former Paralympic doubles medallist is now ranked 47 in the world and will play Germany's 2012 champion Sabine Ellerbrok, a 6-1, 6-1 winner over Japan's Saki Takamuro, in the next round.

Defending champion Yui Kamiji began her campaign for a fifth straight title on home soil with a routine 6-1, 6-1 win over South Korea's Ju-Youn Park.

Lucy Shuker of Britain ended the hopes of another home player by beating qualifier Emi Suda 6-1, 6-0.

There was also double disappointment for the hosts at Dutch hands as Diede de Groot beat Momoko Ohtani 6-2, 6-3 and world number four Aniek van Koot saw off Manami Tanaka 6-0, 6-3.

In the quads competition, Britain's Andy Lapthorne came from behind to beat Japan's Mitsuteru Moroishi 4-6, 6-1, 6-2.

He will now face defending champion and double Paralympic Games champion Dylan Alcott in the last four.

The Australian world number one continued his bid for a third title in a row with a 6-2, 6-2 victory over Greg Hasterok of the United States.

Competition will continue tomorrow.