Hosoishi abruptly had much success at the age of 24; as an "unknown" he defeated a number of "top players" to win the Japan Open.

After his win in Malaysia the legendary Australian golfer Peter Thomson stated that he "is likely to emerge as the number one star on this tour.

Though he continued to play consistently on the leading Asian tours in the 1970s he did not win another significant event.

He entered a sudden-death playoff with Koichi Ono and Isao Katsumata, both of Japan, and Taiwan's Hsieh Yung-yo and Chen Ching-Po.

[4] Hosoishi was considered an "unknown" at the time; his victory against these "top players" was a big surprise.

Hosoishi shot a final round 68, tying the lowest score of the tournament.

On the third playoff hole Gregson hit his approach into a bunker and Hosoishi won the championship.

Within an hour of teeing off, however, Hosoishi settled down with excellent putting and chips shots.

[13] After the round, Peter Thomson wrote in The Age, "Hosoishi outplayed us all, and is likely to emerge as the number one star on this tour.

Australian Stan Peach led by four over Hosoishi entering the final round.

[3] His good play over the course of the year earned him entry to a number of elite international events.

In August, it was announced that he earned entry into the Alcan Golfer of the Year Championship at Royal Birkdale Golf Club in England.

He finished joint runner-up to compatriot Takaaki Kono, five behind, tied for second with South Africa's Hugh Baiocchi.

[19] Later in the month, he represented Japan at the 1968 World Cup held in Rome, Italy.

In 1970, he was one back of Hsieh Yung-yo's lead entering the final round of the Singapore Open.

[21] The following week, he established a "scorching pace" at the Malaysian Open, shooting a bogey-free 65 (−7) to take the solo lead.