Trained by Mitsuru Hashida and ridden by Oisin Murphy, the five-year-old daughter of Harbinger finished with a flourish to capture the Group 1 honours by a length and a quarter from long-time leader Mehdaayih.
The victory was just the second time Japan have won a Group 1 contest in Britain following Agnes World's win in the 2000 Group 1 July Cup at Newmarket.
Deirdre finished sixth in the Group 1 Prince Of Wales's Stakes at Royal Ascot in June with connections blaming the soft ground for her performance. They decided to remain in England, situated at Jane Chapple-Hyam's Abington Place Stables in Newmarket with Deirdre coming to Goodwood Racecourse for an away day last month to gain experience of the course.
The mare, out of the Special Week (JPN) mare Reizend (JPN), is owned by Mr Toji Morita, who owns a family business in Osaka, Japan. His Racing Manager Seiko Hashida Yoshimura, who is also the daughter of the winning trainer Mitsuru Hashida, was thrilled by Deirdre's success.
"That was a special performance from Deirdre. It is fantastic to have a winner at the Qatar Goodwood Festival. This is very important not only for us, but also for the whole of Japan to come over to Britain and have a big-race winner,” said Hashida.
"Today's victory is important for Japan because it showed that it is not just possible to come here and compete, but that it is also possible to win. Hopefully, we can have a good influence on Japanese racing with this win.
"It was a very big challenge to come here. We have been in Britain for three months with Deirdre and we are so pleased that we kept believing in her. We had a lot of support and this has made this victory possible.
"We were just hoping for the best for her today. It was a gloriously sunny day at Glorious Goodwood and everything just fell right for her. Goodwood is a beautiful racecourse. It is very different to Japanese racecourses which are usually oval-shaped. We were sure that she would like this track and it worked out very well. The quicker ground was another important factor for her today and it is very special to win a Group 1 event in Britain.
"We could see at Royal Ascot that she was trying very hard. There was heavy rain there and that did not help her chances.
"A lot of credit has to go to Oisin Murphy. We did not give him any instructions and just decided to let him ride the horse in the way he felt right. He is a brilliant jockey.
"We have not yet decided if Deirdre will return to Japan or whether she will stay over here. We will make that decision in the coming days when we sit down and have a chat about what we should do next. She could possibly stay in Europe.
"Deirdre is a daughter of Harbinger [2010 King George VI & Queen Elizabeth QIPCO Stakes winner] so that is one of the reasons we came over here. After Royal Ascot, we stayed in Newmarket, and thanks goes to Jane Chapple-Hyam. We had very good surroundings and we trained very well coming here. Hopefully, everybody at home [in Japan] was watching," she said.
Deirdre's victory in the Qatar Nassau Stakes was a superb result for her homeland of Japan and a significant one for international racing.
Ridden by Oisin Murphy, the five-year-old mare pulled off a 20/1 shock, but she beat a top-class field fair and square, becoming the first runner and winner for Japan at Goodwood.
The Mitsuru Hashida-trained winner scored by one and a quarter lengths and the same from pace-setting Mehdaayih, the mount of Frankie Dettori, and Rawdaa, ridden by Danny Tudhope.
Murphy, who is leading Britain's Stobart Jockeys' Championship with 86 winners, three clear of Tudhope, formed contacts in Japan during a visit there in January when he rode in a number of races.
He said: "I'm so glad the Japanese have bought a horse here and she has performed. I've been telling people since I came back from Japan of the regard they hold their horses in, and it's fantastic they have won a Group One race here - she was already a Group One winner, but it is great to do it in Britain.
"I can't tell you how pleased and thrilled I am for all the connections.
"Hopefully we will see more horses from Japan coming over. Northern Farm, which bred this mare, has some wonderful pedigrees and this is a huge result. When in Japan I was spoilt because I rode great horses every morning," he said.
Deirdre’s career highlight in Japan came when winning the Group 1 Shuka Sho over 2000m at Kyoto in October, 2017. She has also won two Group 3’s and a Group 2 in Japan.
The mare is well suited to competing outside of Japan with five international starts. She was third to Benbatl in the 2018 Group 1 Dubai Turf (1800m) at Meydan, UAE, and a fast-finishing second when beaten a length by Glorious Forever in the Group 1 Longines Hong Kong Cup 2000m) at Sha Tin, Hong Kong, in December. She was fourth behind compatriot Almond Eye in this year's Group 1 Dubai Turf in March.
"I think to bring Deirdre over here from Japan and win a Group 1 like this, at a great festival, it is fantastic for international racing and for Japanese racing. If we were going to be beaten, I am delighted to be beaten by the Japanese,” said Newmarket trainer John Gosden who trained the runner up.
"I saw Deirdre as a threat today, I have seen her train across the road in Newmarket and I know her form. She is a tough race mare, a real pro, and her owners are the most charming people,” he said.