Oracle Team USA stayed alive in the America's Cup after beating Team New Zealand in race 12 - the only completed race on Thursday.
Later in the day, Race 13 was postponed until Friday after winds exceeded the 20 knots limit in San Francisco bay.
The Kiwis lead 8-2 in the 17-race finals series and need to win only one more race to take the trophy.
Team USA, the defending champions, took Thursday's only race by a comfortable 31-second margin.
They won the start with a shrewd manoeuvre that pushed New Zealand away from the line, and then showed impressive speed on the critical upwind leg before dashing home for the victory.
The Kiwis turned in the latest of several textbook performances in moving to the brink of victory on Wednesday, and seemed to have beaten back an Oracle revival that saw the United States boat win two thrilling races over the weekend.
But Thursday's first race suggested the momentum could be shifting once again as Oracle showed the speed, tactics and boat handling it needs to match the polished Kiwi team.
"We have to finish this thing," said Ben Gordon, a New Zealander who lives in San Francisco. "The boat's are dead even and it's getting a bit dodgy."
There will be two races - if required - on Friday.
Wednesday's second race was also postponed because of a strong breeze and outgoing tide.
The AC72 catamarans can attain speeds of up to 50 miles per hour, but are hard to control and potentially subject to capsize and equipment failure in high winds.
The Kiwis are seeking their third America's Cup, having won in 1995 and in 2000.
America's Cup schedule
Fri, 20 Sept: Race 14 (21:15), *Race 15 (22:15)
Sat, 21 Sept: *Race 16 (21:15), *Race 17* (22:15)
Sun, 22 Sept: *Race 18 (21:15), *Race 19 (22:15)
BBC coverage times
Highlights (all BST)
Fri, 20 Sept - 13:30-14:15 (BBC Two), 14:15-15:00 (Red Button)
Sun, 22 Sept - 14:05-14:50 (BBC Two), 16:40-18:10 (Red Button)