The tournament's return to Royal Portrush for the first time since 1947 has attracted a field including world number two Rory McIlroy and fellow Northern Irishmen Darren Clarke and Graeme McDowell.
Triple major champion Padraig Harrington and US PGA winner Keegan Bradley are also due to take part in the June 28-July 1 event in County Antrim.
"We are preparing for a crowd around the 100,000 mark for the week...and with a particularly large spectator audience expected for the weekend we felt it prudent to stop selling tickets for Saturday and Sunday," championship director Antonia Beggs said.
Portrush is the home town of Clarke who claimed his first major victory in The Open at Sandwich last July.
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