Paul Heckingbottom is adamant Barnsley cannot keep making the same mistakes that they are in pre-season in the Championship.
The Reds had to come from behind twice to draw with National League outfit Guiseley early last week, before being beaten 2-1 at League Two Grimsby Town on Saturday.
And Heckingbottom singled out his central defenders after a handful of mistakes at the back cost his side at Blundell Park.
“Forgot the tactical element at the minute because that will take time,” insisted Heckingbottom.
“The two takeaway messages I gave to the players were a mistake and a set piece cost us.
“You can’t be making mistakes in the Championship and expecting to win.
“I honestly believe we’ll have a good back four this season, with centre backs competing for places.
“They’ve all got different qualities, but second half we were sloppy. Angus [MacDonald] for the goal, Liam [Lindsay] with the pass, Jacko [Adam Jackson] not getting to the ball when it bounced and Ethan [Pinnock] down in the corner, it was just bad decision making.
“They knew that and they’ve held their hands up to that.”
Lloyd Isgrove is loving life back at Oakwell and he doubled his pre-season tally with an easy tap-in early on.
However, a last-ditch Brandon Robinson goal sealed the game for the hosts after Siriki Dembele equalised just after the break.
Sessi D’Almeida had a strong showing in the middle of the park, breaking up the play well and getting stuck in to challenges as he looked back to full fitness.
The Reds controlled the game early on as the new squad seemed to be gelling together nicely.
New signing Liam Lindsay saw an early dink cleared off the line, before the Reds’ upped the ante before the break.
George Moncur, who was a completely different player at the end of last season as opposed to the start, played in Tom Bradshaw who was superbly denied by the Grimsby stopper.
Moments later Moncur beat two defenders and almost created an embarrassing own goal for the Mariners, with Isgrove mopping up from six yards.
Just after the restart Adam Davies was beaten as Dembele slotted home after a wayward MacDonald pass started the move off.
Right-back Andy Yiadom tested James McKeown as he broke past three defenders, with the ‘keeper up to the task of keeping his powerful strike out.
Late on the Reds failed to clear their lines from an in-swinging corner as trialist Robinson won the hosts the match with five minutes left.
Heckingbottom added: “Physically it was a good workout. We built the minutes up for the players.
“We only had three missing out today, so hopefully we’ll get a couple of them back for the next game.”
The Reds will be in action for the first time at Oakwell this season against Coventry City on Tuesday night.
Barnsley starting XI: Davies, Yiadom, Lindsay, MacDonald, McCarthy, Isgrove, Moncur, D’Almeida, Hammill, Mowatt, Bradshaw.
Subs: Townsend, Hedges, Pinnock, Williams, Wardle, Palmer, Jackson, Mallan, Brown, Bird, Wolfe.