The Masters golf tournament at Augusta (GA) National Golf Club is played the first week in April, but many believe that it really doesn’t get exciting until Sunday. “The oft-repeated line here is that the Masters doesn’t actually begin until the back nine on Sunday” was printed in the Dayton (OH) Daily News on April 14, 1980. “IT IS The Gospel according to Bobby Jones that the Masters doesn’t begin until the final nine on Sunday” was printed in the Dayton (OH) Daily News on April 12, 1982. “The saying goes that the Masters doesn’t start until the 10th tee on Sunday” was printed in the Sun Sentinel (Fort Lauderdale, FL) on April 15, 1985.
 
It is not known who originated the saying.
   
     
Wikipedia: Masters Tournament
The Masters Tournament (usually referred to as simply The Masters, or the U.S. Masters outside of North America) is one of the four major championships in professional golf. Scheduled for the first full week of April, the Masters is the first major of the year, and unlike the others, it is always held at the same location, Augusta National Golf Club, a private course in the southeastern United States, in the city of Augusta, Georgia.
         
14 April 1980, Dayton (OH) Daily News, “Sevvy survives back 9” by Gary Nuhn, sports sec., pg. 7, col. 2:
The oft-repeated line here is that the Masters doesn’t actually begin until the back nine on Sunday.
 
12 April 1982, Dayton (OH) Daily News, “No tears: Stadler’s crying days stop after playoff hole earns him the Masters” by Gary Nuhn, sports sec., pg. 1, col. 4:
IT IS The Gospel according to Bobby Jones that the Masters doesn’t begin until the final nine on Sunday.
   
15 April 1985, Sun Sentinel (Fort Lauderdale, FL), “Strange finish allows Langer to win Masters” by Tim Rosaforte, pg. 1D:
The saying goes that the Masters doesn’t start until the 10th tee on Sunday, and if that’s the case, this Masters started with Strange at 7-under par for the tournament and holding a four-shot lead.
 
14 April 1986, Sun Sentinel (Fort Lauderdale, FL), “Add a ‘gee’ to Olden Bear: Nicklaus cards 65 to win 6th Masters” by Tim Rosaforte, pg. 1D:
The old saying goes that the Masters doesn’t begin until the back nine on Sunday.
 
12 April 1987, Asheville (NC) Citizen-Times, “Norman Starts Charge Early” by Doug Mead, pg. 1B, col. 1:
AUGUSTA, Ga.—They say the Masters doesn’t really begin until the back nine on Sunday afternoon. Don’t tell that to Greg Norman, who got an early start here Saturday.
 
10 April 1988, Star Tribune (Minneapolis, MN), “Masterful Finishes: It’s survival of the fittest on the final round” by Jon Roe, pg. 4C:
“The Masters doesn’t really begin until the last nine holes on Sunday,” Greg Norman once said. “It’s when you get to the 10th hole that things really start to happen.”
     
15 April 1991, Philadelphia (PA) Daily News, “Woosnam rises to the occasion” by Mike Kern, pg. 89: 
The axiom that the Masters doesn’t really begin until the leaders reach the 10th tee on Sunday was never more evident.
     
13 April 1992, Philadelphia (PA) Daily News, “Fred wins Masters by a couple” by Mike Kern, pg. 94:
They say that the Masters doesn’t really begin until the leaders reach the back nine on Sunday.
   
Google Books
Golf Courses of the PGA Tour
By George Peper
New York, NY: Harry N. Abrams
2004
Pg. 107:
There’s an old saying that The Masters doesn’t really begin until the last nine holes on Sunday, and there’s no question that the inward side of the Augusta National— even after all the alteration and toughening— still provides high drama, as it did in 2004 when Phil Mickelson charged home in 31 strokes to edge ...
   
Google Books
Tiger Woods:
A Biography
By Lawrence J. Londino
Westport, CT: Greenwood Press
2006
Pg. 84:
The general wisdom is that the Masters doesn’t really begin until the back nine on Sunday.
   
Google Books
Moment of Glory:
The Year Underdogs Ruled Golf
By John Feinstein
New York, NY: Back Bay Books/ Little, Brown and Company
2010
Pg. ?:
One of the oldest clichés in golf is that “the Masters doesn’t start until the back nine on Sunday.”
 
Twitter
Kerry Kenny
@KerryBKenny
As the old adage goes, the #Masters doesn’t really begin until the back 9 on Sunday…
1:59 PM - 10 Apr 2011
     
Google Books
The Magnificent Masters:
Jack Nicklaus, Johnny Miller, Tom Weiskopf, and the 1975 Cliffhanger at Augusta
By Gil Capps
Boston, MA: Da Capo Press
2014
Pg. 243:
It’s not known when or who coined the phrase, “the Masters doesn’t begin until the back nine on Sunday,” and whether or not it was widely acknowledged before or after 1975.
 
Statesboro (GA) Herald
The shots that will win the Masters
MIKE ANTOHNY
.(JavaScript must be enabled to view this email address)
Updated: April 11, 2019, 12:31 a.m.
As the old saying goes, The Masters doesn’t really begin until the second nine on Sunday.