O'Brien try the difference in dour Welsh derby
Scarlets had trailed throughout the match but conjured up a late piece of magic through O’Brien which Dan Jones converted to add to his three penalties.
It was rough justice on Ospreys, who had to surrender home advantage as their Liberty Stadium pitch was being re-laid.
Welsh international Johnny McNicholl was a late withdrawal for Scarlets with O’Brien replacing him at full-back.
Ospreys lost a couple of line-outs which allowed their opponents to exert early pressure but Scarlets could not capitalise despite mounting a succession of close-range forward drives.
It was therefore against the run of play when Myler kicked his side into the lead with a straightforward penalty.
This was one of six penalties conceded by Scarlets in the first 16 minutes and they suffered a further setback when wing Tom Rogers was forced to leave the field with a leg injury.
Myler’s penalty was the only score of a featureless first quarter before the game sprung into life with an excellent solo try from Morgan-Williams.
Scarlets lost possession at a ruck 35 metres out and the scrum-half sold a dummy before racing away and outpacing O’Brien for a superb score.
Jones put Scarlets on the scoreboard with a penalty but then missed from 30 metres with his kick rebounding off a post. His side nearly made amends when Steff Hughes put in a well-judged cross-field kick but Steff Evans was unable to gather with not a defender in sight.
With the last kick of the half, O’Brien missed with a long-range attempt so Ospreys were able to retain their 8-3 lead at the interval.
Two minutes after the restart, Myler had an opportunity from a similar range and he made no mistake before he and Jones exchanged penalties.
With nine minutes remaining, Scarlets scored the crucial try. Poor kicking from their opponents had surrendered territory and O’Brien capitalised by racing past two defenders to score with Jones’ conversion proving decisive.
Sign up to our mailing list for a weekly digest from the wide world of rugby.Sign Up Now