The decision to utilise the first Reserve Day of the Louis Vuitton Cup proved to be a far-sighted one by Race Director, Iain Murray, as perfect conditions greeted INEOS Britannia and Luna Rossa Prada Pirelli today for the fourth day of their epic, locked-in battle to win the Louis Vuitton Cup.

The ‘Garbi’ south-westerly wind was in, and, crucially, just below the wind-limit of 21 knots. With relatively flat water the two starts both got underway on time, with the racing taking place beneath a cloudless sky and with the stunning Barcelona beachfront as a shimmering backdrop. The British and Italian fans who have travelled to Barcelona packed the Race Village and Fanzones, cheering on their countrymen passionately and colourfully, mirroring the on-water action and tensely lapping-up the action.

With the series tied at 2-2 at the start of the day, the British Challenger of Record, INEOS Britannia, took the tally to 3-2 after an opening race where accuracy of execution was rewarded. Sir Ben Ainslie pulled off a classic match-race move deep in the pre-start box, powering over the bow of Luna Rossa in the final 30 seconds to the start.

The subsequent water and wing wash of the fast-driving British helped to force the Italian boat off its foils as it turned up behind Britannia. The Luna Rossa sailors quickly recovered, but the Britannia crew were able to execute an unchallenged time-on-distance run back to the line and start ahead.

Any ideas that the race might be done and dusted at this point were quickly dispelled. Over the subsequent eight legs, the boats seemed to be tethered by elastic as they nipped, tucked and covered, never more than a few seconds apart. For the aggressor, Luna Rossa, it was about staying in touch and waiting to pounce on any mistake from the British.

Such an opportunity very nearly came at the rounding of the final leeward gate, when, with Sir Ben Ainslie steering around the starboard marker, the British boat made a major sideways skid, critically washing-off speed. Suddenly the two boats were into a classic upwind match race, boat-for-boat but with INEOS Britannia’ marginally holding the aces as they steadfastly countered the Italian's every attack.

After some close quarters action over at the right boundary, Ainslie and co-helmsman Dylan Fletcher tactically out-positioned the Luna Rossa pairing of Jimmy Spithill and Francesco Bruni on a long starboard layline, to round the final windward gate with an eight second lead, before gybe covering in precise fashion down the final run to the finish. Crossing the line ahead with a 12-second delta, INEOS Britannia claimed the day’s first blood.

Any momentum from that hard-fought British victory was effectively negated at the end of the second race, in which the wind clocked further to the south-west making getting ahead at the start paramount to gaining control. Luna Rossa came off the line to windward and after an initial drag race to the left boundary, bailed out first and arm-wrestled their way back to the right boundary.

With right-of-way advantage, Luna Rossa capitalised on the tack back and – with INEOS Britannia now to leeward – metre-by-metre they eked into a lead that they would never give up, after gaining further by shepherding INEOS Britannia to the left of the course, onto the port layline, in the final approaches to the windward mark.

After that fight for supremacy, the rich got richer on a very readable racetrack where tactical positioning could be dictated by the leader. INEOS Britannia tried to get out of phase at times, looking for passing lanes out on the left of the racecourse, but they were losing gambles and despite keeping it close, by the final downwind leg the British were praying for a miracle that never came. Luna Rossa powered across the finish line at 51 knots to record a 17 second win and level the Louis Vuitton Cup Final at 3-3 in this first-to-seven-points series.

Dylan Fletcher, port helm for INEOS Britannia came ashore after racing, and reflected on a day that ended all square but could easily have been different, saying: “I think the racing really showed how evenly matched the boats are in those conditions. It was kind of won or lost on the start. In that second one we thought we should've done enough, but they managed to work a nice little shift on that right hand side and that just seemed enough to get ahead – but it's close action.”

Asked how this contest will be split, Fletcher said: “I think we’re seeing that it's going to be down to fine margins and which team keeps learning, keeps progressing, and executing on the water. Obviously, it was a tough race, that second one, but feels like we're learning every day and the boat’s getting faster every day and we’ve just got to take that confidence and keep pushing in the pre-start.”

For Francesco Bruni, the port helm for Luna Rossa Prada Pirelli, there was an air of confidence having kept it close in the first race and then stepped out in the second. “Well definitely we felt that we have some speed. The boat is going well. We are very pleased with the performance of the boat and how we are going. A little mistake in that first start, where we felt that we had a good position and you know it takes very little to lose control of these boats. So I think we are optimistic about how things are going, but we know it's going to be a very hard battle.”

Talking about the splashdown in the pre-start of the first race today, Bruni confirmed that one of the foils went into ‘cavitation’, but when further asked just how this contest will be decided, he added: “I think it’s going be consistency until the end. It's going to be a big battle for sure, it's not going to be easy, but we are we are ready for the fight, and we like to fight."

Quite where the back-and-forth deadlock between these two teams will be broken is hard to discern. Slugging away like two heavyweight boxers, after six rounds the judge’s scorecards are all square, and there are simply no discernible performance differentials between them.

The series remains anyone's to win and both crews know all too well that it could be lost in a heartbeat. Match-racing at speeds in excess of 50 knots is always a recipe for jeopardy, but with such similar performance profiles this could ultimately come down to which team wants it most. One of the most evenly-matched Louis Vuitton Cup Finals of all-time, this looks set to go all the way.

The ultimate reward of taking on the Defender, Emirates Team New Zealand, in the Match for the Louis Vuitton 37th America's Cup might feel some distance away right now, but these two fantastic teams are serving up a Barcelona spectacle worthy of the greatest of sporting competitions. Someone has to deliver the knock-out blow in the coming days – but who that will be is anyone’s guess right now.

Racing in the Louis Vuitton Cup Final series in Barcelona continues tomorrow, Tuesday October 1, with two more races scheduled to begin at 1400 CET, when more breezy conditions are expected.