Erik ten Hag rues dropped points as United lack ruthless edge
Dutchman Ten Hag was on the cusp of becoming the first Manchester United manager since the great Alex Ferguson in 2009 to win 10 successive games as his side led 1-0 at Selhurst Park in the 91st minute.
Another couple of minutes and United would have gone second in the Premier League, six points behind Arsenal ahead of Sunday's showdown with the leaders.
But then Olise cooled the title talk with a magical free kick that left David De Gea clawing at thin air and United paying the price for a lack of killer instinct.
United will feel short-changed having controlled large swathes of the game, although Ten Hag said they had themselves to blame for not being hungry enough to add to the lead given to them by Bruno Fernandes late in the first half.
"We have to invest more to get that second goal and then not be in that situation that a lucky moment costs you two points," Ten Hag told the BBC. "We were 1-0 up. In the second half we had a lot of space to kill them and go for the second.
"I never saw we really went for the second goal."
To add to United's woes they had a justifiable penalty claim turned away and, more damagingly, influential Brazilian midfielder Casemiro was booked late on for a rash challenge and he will now be suspended for the trip to Arsenal.
"He's a really important player for us and a reason we're in this position," Ten Hag said.
"But last time we beat Arsenal without Casemiro. We need to do it again."
Despite the disappointment, United's run of form has lifted them to a position few imagined was possible earlier this season and Ten Hag said the focus was now on Arsenal.
"It happened. You can't change it. We're looking to Arsenal and to make a proper plan. The players have to make sure they're ready. It's fantastic to play such games."
While Ten Hag tried to play down the loss of Casemiro for Sunday's clash, keeper David De Gea admitted it was a bitter blow and he also questioned why United were playing in midweek.
"Big blow to lose Casemiro for Sunday. I don't get it why Arsenal don't play as we have to play in the same week and they don't," he said. "Now we are missing one of our best players.
"I don't understand. Now we miss him for a big game and it is a big loss for us."