His first international outing came in
middle-distance events at the
2007 Asian Indoor Games. He failed to finish in the
800 metres, but set a
national indoor record of 4:11.28 minutes in the
1500 metres heats. He won his first medal at the competition in the
4 × 400 metres relay, taking the
gold alongside
Hamdan Al-Bishi,
Ali Al-Deraan and
Hamed Al-Bishi. In the 2008 season he was based in
California and began to run in the
200 metres and 400 metres instead, setting best times of 21.80 and 46.45 seconds in the events. Masrahi won the national title over 200 m in 2009 and improved his 400 m best to 45.84 seconds in Riyadh, gaining the
"B" qualifying standard. He represented Saudi Arabia at the
2009 World Championships in Athletics, but was knocked out in the
400 m heats. He was the
bronze medalist in the distance at the
Arab Athletics Championships and also won the relay title with Saudi Arabia. The
2010 Asian Games was his focus for the next season and he gained selection after winning a 200/400 m double at the national championships. The next year, he won the 400 m gold medal at the
2011 Asian Athletics Championships in
Kobe, Japan, and also won a
silver medal in the relay. In 2014, he won the gold medal for the men's 400 m in 44.6 sec. He set his personal best, the Asian record during the qualifying heats of the
2015 World Championships, finishing barely ahead of
Rusheen McDonald who was credited with the same time, 43.93 which at the time ranked both men in the top dozen in history. With two more rounds to run, McDonald was unable to qualify for the final, while Masrahi did, but his remarkable speed was not present in that final where even his personal best would only have been good enough for fourth place. ==Anti-doping violation==