American teenager Michael Phelps broke his own 200 metres individual medley world record again on Saturday as he became the first man to win five titles at a U.S. national championships.

The 18-year-old won the final in a time of one minute 55.94 seconds, taking .10 of a second off the previous record he set at the world championships in Barcelona on July 25.

It was the fourth time Phelps had lowered the record in the event in the last six weeks -- in total taking more than two seconds off Finn Jani Sievinen's 1:58.16 which had stood since 1994.

Saturday's success at College Park, Maryland came after victories in the 100, 200 and 400 metres freestyle and the 200 metres backstroke -- all in personal best times.

Two women -- Tracy Caulkins in 1978 and Natalie Coughlin last year -- have won five events at the U.S. nationals, while the previous men's best of four was shared by Johnny Weismuller, Mark Spitz and Tom Dolan.