Both Smith and Russell Peters, in DBS, ended the day with 39 points, but Smith mastered the tricky, gusting winds to win two of yesterday's three races, most importantly the third, which decided the points.
This gives Smith two grand prix wins to Peters' one going into the final regatta in Belfast at the end of August. The improving Roger Yeoman posted a third place in Save & Prosper, ahead of Eddie Warden Owen in Hoya, Glyn Charles in United Airlines, and Pete Newlands in Mobil.
In a more gentle Solent, the world champion Bruce Owen was at last able to make some good work count, winning both the final races in the Six- metre National Championships, being staged as part of MDL Hamble Week.
But it was never going to be enough to pull back Tony Canning, who had sailed strongly to win the first four races and was second in the final two. That gave Canning the title by three points, with Owen second and Tom Richardson third.
In the BT Challenge the leading yacht, Mike Golding's Group IV, was just 490 miles from the finish of the last leg from Boston to Southampton. He should arrive tomorrow or Wednesday, but fickle winds are leading to frustrating times for some of the other 13 competitors.
Light winds also plagued the Royal Ocean Racing Club fleet from Cowes to St Malo, with Kit Hobday in Independent Bear winning Class One from the Swan European regatta champion, Terry Robinson, in Assuage.
FRONTERA ULTRA 30 GRAND PRIX: Round Three (at Cardiff): Final results after eight races: 1 Frontera (L Smith) 39 pts; 2, DBS (R Peters) 39; 3 Save & Prosper (R Yeoman) 27; 4 Team Hoya (E Warden Owen) 25; 5 United Airlines (G Charles) 23; 6 Team Mobil (P Newlands) 15.