They won the first race by 72sec and were a similar distance ahead going into the last lap of the second only for conditions to become more fluky, allowing Spain's Luis-Martinez Doreste not only to catch and pass them but also to pull out a 97sec margin in the last half mile.
However, a first and a second had Merricks and Walker, with crew Mark Tomson and Nick Powell, firmly at the head of the 47-boat fleet after a frustrating start to the event.
On the first, there was no wind, no racing. On the second, only one race was completed and that was declared void by the jury after a complaint, led by Britain's Matt Humphries, that disqualifications that should have taken place had been overlooked. The race committee agreed and accepted responsibility.
The British national champion, Mike Lennon, is locked in a private and separate battle here with the aim of beating the European champion, Giorgio Zuccoli of Italy, to earn the right to represent Europe against the Americans at Key West in January. Lennon's 24th and 10th to Zuccoli's eighth and 18th keeps him in the hunt with perhaps only five races left in a series curtailed from its original 12.