Wasn’t Dan Marino’s last ever game for Miami a clunker? Something like under 100 yards passing for the entire game, and having to beg Jimmy Johnson to let him go back out for the second half?
EDIT: Found it here. 11-25 passing for 95 yards, one touchdown. Miami got pasted by Jacksonville 62-7.
Of course, the top of his game was happening with the Lions so he still might count. 
Phil Niekro was brought back to Atlanta for one final start after being released a month earlier at age 48. In three innings he gave up 5 runs, 6 hits, 5 walks and no strikeouts. At least financially it was a good decision by Atlanta. They drew 26,019 fans for the September 27, 1987 game.
Don’t believe all the movies that have Babe Ruth retiring after hitting three home runs in a game as a Boston Brave. He was tempted to but since he was a financial draw, he played a few more games, going hitless in his last game May 30, 1935
On the other hand, the KC A’s brought the long-retired Satchel Paige into a game at the age of 65. Three shutout innings.
He’s listed as 58 at that time, but his true age very well could have been closer to 65. I was listening to an old interview with Buck O’Neil over Christmas on NPR, and he talked at length about Satchel. His description of that game was fantastic. That wasn’t a very good Red Sox team, but holy hell - the man was OLD!
I don’t know if it qualifies as the worst last performance of a great athlete, but the best thing you can say about Johnny Unitas’ last season with the San Diego Chargesis that it was pretty forgettable.
While we’re talking about boxers going out badly, I’d like to nominate a boxer who won his last fight: Luis Resto.
The reason why is because of how he won:
I know that the OP specified super-star athletes, but Billy Collins had superstar potential and it was taken away from him by two unscrupulous people. Yet he stood there and took it, going the distance against a guy who was essentially hitting him with bricks since the wraps were also soaked in Plaster of Paris.
Steve Carlton got criticism his last few years for hanging on too long. His final appearance reflected it: 5 IP, 9 hits, 9 runs (8 earned) 3 walks 4 strikeouts, 2 home runs on April 23, 1988
Walter Johnson’s final appearance is noteworthy because one of the greatest pitchers ever was used as a pinh hitter (he made out). The game was September 30, 1927: the same one Babe Ruth hit his 60th home run.
Arnold Palmer kept playing some PGA Tour events well after he was competitive. He missed his last 43 cuts in a row. His last cut made was in 1993 and he continued playing 3 -5 tournaments/year until 2004. He shot 84 - 84 at the Masters in his last two rounds on tour.
That’s the one I was going to mention. I don’t remember Marino’s performance specifically, but it was his last game and “clunker” is hardly a strong enough word to describe it.
For god’s sake, the field sprinklers even came up and sprayed the Miami guys, adding absurd insult to injury. Of all games for that to happen; it just seemed so symbolically sad.
But as I said, I don’t know if Marino’s performance was particularly awful.
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Of course, playing 3-5 golf tournaments a year is many, perhaps even most, athletes’ definition of retirement. I don’t know about Mr. Palmer, but it’s possible he wasn’t thinking of these as performances, but more like the equivalent of playing catch in the parking lot before heading in to the luxury box to watch the not-yet-retired athletes play.
Why not use him as a pinch hitter? He batted .348 that year and by other metrics was clearly superior as a hitter than a pitcher.
Did Palmer ever join the Senior Tour? That’d be a decent line to draw for him.
How do we classify Tom Watson’s 2009 British Open?
Bobby Riggs?
Yes, Arnold joined the senior tour when he turned 50. It can even be argued that there would be no Senior tour if there was no Arnold Palmer.
Arnold Palmer’s last regular event on the Sr tour resulted in rounds of 89-84-86 in the 2006 Constellation Energy Classic. That tournament, like most Sr tournaments has no cut. Palmer came in last (78th). The guy that came in next to last was 29 shots ahead of him.
Incredible, but not a complete surprise to me.
Tom Watson has not retired from PGATour golf. He was 59 at the time, and obviously still competitive, given the right course and conditions. The British Open courses meet those criteria. Watson just won the Sr event in Hawaii this past weekend, with an incredible -22 par in just three rounds. Watson is not a full time player on the Sr Tour. He normally plays about half the events.
Watson will continue to play the Masters and British Open for a few more years. Maybe a couple of other events on the PGATour. Interestingly, he is scheduled to be in Dubai next week to play in one of the European Tour biggest events.
As usual for these threads, I’ll add a good horse racing example:
Lady’s Secret, a gray daughter of Secretariat, was voted the 1986 Horse Of The Year in the US. However, she was not the same in 1987, and finally dropped in class to an allowance race at Saratoga during that summer, winding up facing a field she could beat even if she ran backwards. However, when the gates opened, she headed towards the outside fence and forced her jockey to pull her up and out of the race. Her trainer tried to get her mind back on racing, but she was retired soon after this incident, so the non-effort was her last start.
Player of the tournament gets the Golden Ball. Top scorer gets the Golden Shoe (I swear it used to be called the Golden Boot).
Like WTF? You are kidding, right?
AM Archive - Friday, 2 March , 2001 00:00:00
Reporter: Anne Barker
COMPERE: Tens of thousands of people lined the streets of Adelaide last night to farewell Don Bradman. Family and friends, including the Prime Minister and Governor General, attended the private funeral, while the public were invited to pay their respects as the funeral cortege wound its way through the city.
…
Graeme ‘Changa’ Langlands, rugby league fullback for St George. Australia captain, Australian coach, RL Hall of Fame and Team of the Century.
He played his last match in the 1975 grand final v Easts.
A pre game pain-killing injection for a groin injury went wrong and with deadened leg nerves he was a hobbling passenger for the whole game. To highlight his difficulties, in a sponsors deal Langlands wore white boots. The 38-0 scoreline was the most lopside result in the league’s history.
I hope so. Schoolchildren in India still learn Bradman’s name.