“"Austin powers a home run!*" (Austin Kearns)”

As quoted in “Clouter Clemente: Popular Buc; Rifle-Armed Flyhawk Aims At Second Bat Crown” by Les Biederman, in The Sporting News (September 5, 1964)
Baseball-related, <big><big>1960s</big></big>

Speaking with reporters after simultaneously reaching several milestones with one swing of the batː 2,000 career hits, 23 home runs (matching his previous high in 1961), and, for the first time in his career, 100 RBIs or more for a season; as quoted in "Clemente's 2,000th Puts Bucs On Top" https://news.google.com/newspapers?id=kbIiAAAAIBAJ&sjid=ZbMFAAAAIBAJ&dq=men-base-concerned-driving-run-getting-no&pg=755%2C515794 by Jeff Meyers (UPI), in The Beaver County Times (Saturday, September 3, 1966), p. C-1
Baseball-related, <big><big>1960s</big></big>, <big>1966</big>

BBC (1979); reported in John Blundell, Margaret Thatcher: A Portrait of the Iron Lady (2008), page 193.
First term as Prime Minister

The earliest quotes similar to this are presented as unattributed folk wisdom, such as this example from 1959:
As Brother Allen of Newsweek indicated, it has been fun, but don't try to rest on your laurels. Always remember, “YESTERDAY’S HOME-RUN DOESN’T COUNT IN TODAY’S GAME,” and today’s game is well under way.
The quote does not begin to be attributed to Babe Ruth until the 1980s, nearly 30 years after its first appearance.
Disputed
Source: F. N. Abbott, "On Your Marks", in [The Palm, vol lxxix, no. 1 (February 1959), Harry L., Bird (ed.), 1959, Champaign, IL, Alpha Tau Omega, 17, http://hdl.handle.net/2027/uiuc.1744313v0079?urlappend=%3Bseq=19]
Source: https://books.google.com/books?id=cQsKAQAAMAAJ&dq=%22Yesterday%27s+home+runs%22&focus=searchwithinvolume&q=Ruth

On his chances for a third consecutive NL batting title; as quoted and paraphrased in "Clemente Not Thinking of Batting Title" by Milton Richman, in The Cumberland Evening Times (Tuesday, March 15, 1966), p. 12
Baseball-related, <big><big>1960s</big></big>, <big>1966</big>
Context: “I never think about that before the season. Toward the end of the year I start thinking about it. Not before. I did it last year by just meeting the ball,” he said. “I didn’t swing hard at all. I think I’m going to do the same thing this year. We have two good hitters behind me now and I don’t have to swing so hard.” He means Donn Clendenon and Willie Stargell. The two hit a total of 41 homers to Clemente’s 10 last year. “They always say we need someone to hit home runs. We got some guys who can now. I don’t care for home runs. I showed ’em I could do it when I hit 23 in 1961. Home runs aren’t that important, though. Not to me, anyway.”

As quoted in Weird Ideas That Work : 11 1/2 practices for promoting, managing, and sustaining innovation (2001) by Robert I. Sutton, p. 95

On the two players deemed by Berra the most underrated of his era; as quoted in The Greatest Team of All Time: As Selected by Baseball Immortals from Ty Cobb to Willie Mays, p. 13.

Calling Ozzie Smith's 9th inning home run off Niedenfuer in Game 5 of the 1985 National League Championship Series.
1980s