1977 Nielsen aged just 17, signed for
Wolverhampton Wolves for the
1977 British League season recording a healthy 7.25 average.
1978 Nielsen won his first Danish Championship and rode in the
1978 European Under-21 Final at the
Pista Olimpia Terenzano in
Lonigo, Italy where he finished 5th with 11 points. The European U/21 Championship was later renamed the World U/21 Championship in 1988. He topped the Wolves averages in just his second year with them.
1979 Nielsen won the
World Pairs with Ole Olsen and finished runner-up to
Jan Andersson in the Scandinavian final. In his third season with Wolverhampton he finished 5th in the
1979 British League season averages and topped the Wolves averages.
1980 Nielsen reached his first World individual final at the
1980 Individual Speedway World Championship, finishing 11th in Gothenburg. He had won the Scandinavian final on his way to the final. During the
1980 British League season he topped the averages on 10.69 riding for Wolves. After the season had ended he put in a transfer request but Wolverhampton then withdrew from the British League.
1981 He appeared in his second World final at the
1981 Individual Speedway World Championship, where he improved two places on the previous year, finishing in 9th place at Wembley Stadium.
1984 A winner of the Scandinavian final on the way to his fifth world final at the
1984 Individual Speedway World Championship, where he finished runner-up to his great rival Erik Gundersen. Nielsen defeated American
Lance King in the silver medal run-off. Earlier in the year Nielsen was signed by Oxford Cheetahs on their return to the British League for a record £30,000, Oxford also signed Simon Wigg for £25,000,
Marvyn Cox for £15,000,
Melvyn Taylor for £12,000 and
Jens Rasmussen. Nielsen topped the league averages with 10.76.
1985 Nielsen won the Danish final with a perfect 15 point maximum but finished runner-up once again to the defending champion Erik Gundersen in the
1985 Individual Speedway World Championship. He helped the Oxford Cheetahs team win the
league and
cup double during a
1985 British League season. Nielsen topped the league averages with an incredible 11.35.
1986 After winning both the Danish and Nordic qualifying finals, Nielsen finally won his first world title after finishing in second place during the two previous Championships. In the
1986 Individual Speedway World Championship he lost his first ride to Erik Gundersen but then won his next four rides to be crowned the champion. Fellow Dane Jan O. Pedersen took silver and England's
Kelvin Tatum took the bronze while Gundersen faded into tenth place. Despite his rivalry with Gundersen he teamed up with him in the World Pairs winning the gold medal. He helped the Oxford Cheetahs team win the league and cup double for the second consecutive season during a
1986 British League season. Nielsen topped the league averages with a record 11.57 and won the
British League Riders' Championship, held at
Hyde Road on 12 October.
1987 Nielsen won his second individual world crown by winning the
1987 Individual Speedway World Championship. In a two-day final in Amsterdam, Nielsen trailed after day one by 1 point to Erik Gundersen and the American
Sam Ermolenko. However, in trademark style Nielsen produced a 15-point maximum on day two to wrap up the World Title, with Gundersen claiming silver and Ermolenko bronze. He also won a third World Pairs and third Danish title and the prestigious
Golden Helmet of Pardubice in
Czech Republic (one of the world's oldest speedway races). In the
1987 British League season Nielsen finished top of the British league averages (11.38) for a remarkable fifth season running and retained the British League Riders' Championship.
1988 Nielsen was denied a third world title in his home country at Vojens in the
1988 Individual Speedway World Championship. The Gundersen-Nielsen rivalry continued with both finishing on 13 points to tie for the lead of the Championship. However it was Gundersen that won the toss to choose his starting gate for the run-off. He chose the outside and on a wet track he won his third title by defeating Nielsen in the run-off. Nielsen won a fourth World Pairs and extended his average topping record, a sixth consecutive season during the
1988 British League season.
1989 A third World title at the
Olympic Stadium in
Munich was well deserved after a 15-point maximum. Nielsen joined fellow Danes Ole Olsen and Erik Gundersen as a three time Speedway World Champion. Nielsen also helped Oxford Cheetahs to another title and topped the averages for the seventh season running, during the
1989 British League season. In a memorable season he also won a fourth consecutive World Pairs (fifth in total).
1990 Nielsen finished fourth at the
1990 Individual Speedway World Championship and was champion of Denmark for the fourth time. Nielsen topped the league averages for the eighth season running and last time during the
1990 British League season. His consistency that led to being the top rider for eight seasons running was a unique achievement. He won a fifth consecutive World Pairs (sixth in total). He also won the British League Riders' Championship for the third time.
1991 He won the bronze medal run-off beating Tommy Knudsen at the
1991 Individual Speedway World Championship in Gothenburg. There was consolation in winning a sixth consecutive World Pairs (seventh in total and a record for any rider).
1992 Nielsen failed to qualify for the world final for the first time since 1979 after finishing 12th in the Nordic Final.
1993 Neilsen had another excellent performance in the
1993 Individual Speedway World Championship but was unable to win the fourth title he was seeking, he had to settle for the runner-up position behind Sam Ermolenko. He was champion of Denmark for the fifth time. He was forced to leave his beloved Oxford Cheetahs following their decision not to compete in the top division, he joined the
Coventry Bees.
1994 Nielsen just failed to win his fourth World title in the
1984 Individual Speedway World Championship after losing a run-off to Swede Tony Rickardsson in the last ever one-off race final. It was also the sixth and last time he was champion of Denmark and his last season in the British leagues.
1996 Nielsen was set to win his fifth world crown with a nine-point lead going into the last of the six events at Vojens in the
World Championship Grand Prix series. However
Billy Hamill won the event gaining 25 points and Nielsen only managed 14 points leaving the Dane two points behind the American in the final standings.
1997 During the
1997 Speedway Grand Prix Nielsen won the
1997 Speedway Grand Prix of Germany but finished 7th in the World title standings behind
Greg Hancock.
1998 During the
1998 Speedway Grand Prix Nielsen won the
1998 Speedway Grand Prix of Denmark but finished fourth in the World title standings behind Tony Rickardsson. He won his second Golden Helmet of Pardubice in the Czech Republic.
1999 In his last World Championship during the
1999 Speedway Grand Prix Nielsen won the
1999 Speedway Grand Prix of Poland II and won the bronze medal in the World title standings behind Rickardsson. ==Retirement==