A 3-1 away win over a 10-man Borussia Dortmund ensured Ajax booked a berth in the last-16 as they finally broke down a resolute German side who played down to 10 men for over an hour of the Group C clash.
But Ten Hag was quick to point out the errors that might have cost his team the game before they rallied to score three times in last 19 minutes and take all the points.
“If you want to go far as a team, you have to be critical,” he told Dutch television.
“You can do that better after a win, and after qualifying for the next round. But in the first half we made big mistakes and gave the opponent power in their counterattack. Dortmund have good players and a good team and are strong on the transition. We were far too impatient and lost too much ball, and so we kept having to track backwards.”
It was the first time Ajax have won their first four games in the Champions League group phase, eclipsing the three victories they posted at the start of 1995/96 competition.
“That shows that we are doing well,” added the coach, never one to mince his words.
“We can show great football, but we can also play badly like in the first half against Dortmund. But we have shown character and resilience. We kept a cool head.”