In 1997, Nielsen returned to the Sydney Kings and won the NBL Rookie of the Year Award.
He played a further seven seasons with the Kings and helped the club win championships in 2003 and 2004.
In 244 career games for the Kings over nine seasons, he averaged 17.5 points, 8.0 rebounds, 2.6 assists, 1.0 steals and 1.5 blocks per game.

In 2004, Nielsen began a decorative European career playing for PAOK Thessaloniki in Greece, Lietuvos Rytas in Lithuania, Valencia in Spain, Olympiacos Piraeus also in Greece, and Khimki in Russia.

On 10 October 2013, Nielsen was named in the Sydney Kings 25th Anniversary Team.
In 1997, Nielsen returned to the Sydney Kings and won the NBL Rookie of the Year Award. He played a further seven seasons with the Kings and helped the club win championships in 2003 and 2004. In 244 career games for the Kings over nine seasons, he averaged 17.5 points, 8.0 rebounds, 2.6 assists, 1.0 steals and 1.5 blocks per game.
In 2004, Nielsen began a decorative European career playing for PAOK Thessaloniki in Greece, Lietuvos Rytas in Lithuania, Valencia in Spain, Olympiacos Piraeus also in Greece, and Khimki in Russia.
On 10 October 2013, Nielsen was named in the Sydney Kings 25th Anniversary Team.
Matthew Nielsen