Callum Davidson pointed to “unacceptable” basic mistakes after St Johnstone went down 3-2 against Hearts at Tynecastle.
The Perth boss was particularly frustrated with how the home side’s winning goal came about with less than 10 minutes remaining.
Davidson said: “I’m furious. My team gave me so much but when you make basic, basic mistakes like, don’t organise and don’t do the right things, it’s unacceptable.
“If we’d been beaten by a goal into the top corner, fair enough, but that wasn’t the case.
“It was a penalty all day long. Graham (Carey) brings it down for him and Gordy has to stay on his feet. But we’ve got to organise better. It’s something I’m going to have to look at.”
Saints had taken the lead through Graham Carey but the hosts were then ahead not long after the half hour mark.
Andy Considine had the Perth men level at 2-2 before Shankland claimed the points.
Davidson said: “In the first half we got a goal up but let them back in.
“I made changes for the second half and we started it pretty well and got our goal. We’d worked so hard to get back into the game.
“That was from a corner and then five minutes later, we get another corner and take it short! At the moment I’m a bit raw – emotions are a bit tender.
“There have been three games when we should have taken something – Hibs, Aberdeen and this one. That’s what is annoying me most at the moment.”
Melker Hallberg, who was the skipper, was forced off in the first half after blocking a free-kick.
Davidson confirmed he is fine and added: “It was a big blow to lose him. We’ve got Murray (Davidson) and Cammy (MacPherson) out.
“Young Daniel (Phillips) is probably playing a little bit earlier than I’d have wanted because of fitness and sharpness levels.
“I thought we rallied well second half when Ryan McGowan won more second balls in the middle of the park.
“I couldn’t afford to get Daniel sent off so I made a few changes, which I thought worked.”
