The 25-year-old South African won the final three events on his factory Yamaha to edge out KTM's Mike Alessi, Honda's Andrew Short and Kawasaki's Tim Ferry in one of the best battles in series history.
It marked the second American motocross title for Langston. He won the AMA Motocross Lites class (then called 125ccc Motocross) in 2003. Prior to coming to America he also clinched the FIM 125cc World Motocross Championship in 2000.
Langston ran sixth in the point standings as late as round seven in late July. But then made an amazing turnaround and scored two seconds and three firsts in the final five rounds to complete his championship rally.
Grant led by just eight points from Short entering a thrilling climax to the AMA outdoor campaign but with his rival only able to take fifth position overall, Langston ended his first season in the class and maiden year with Yamaha 16 points over Alessi and 18 points in front of Short.
"I really didn't think I would be a factor in the championship mid-way through the season," confessed Langston, who only won his first AMA Motocross class national on August 26. "My team worked so hard all year. When we got the new 2008 Yamaha I just seemed to gel with it. To come back and win this title is a great feeling. Every week I kept chipping away. The championship was a like a carrot being dangled in front of me. Once I could see the carrot I got on a roll but I don't think in motocross that it's ever a done-deal. Anything can happen."
Langston's title gave Yamaha its sixth AMA Motocross Championship and its first since Doug Henry won the series in 1998. Langston also becomes the first rider to win the title in the post Ricky Carmichael era. Carmichael won a series-leading six rounds this year, but raced just half the events as he moved toward a new career in stock car racing.
A gracious Langston also recognised James Stewart, the overwhelming pre-season favourite, after winning at Glen Helen. Stewart injured his knee at Washougal and was forced to sit out the rest of the season.
