Frank de Boer acknowledged the Netherlands must tighten up after letting slip a two-goal lead before eventually overcoming Ukraine 3-2 in their Euro 2020 opener.
The Netherlands appeared to be in complete control of the Group C clash in Amsterdam when Georginio Wijnaldum and Wout Weghorst scored in a six-minute burst early in the second half on Sunday.
However, Andriy Yarmolenko's brilliant curling strike from distance halved the deficit, with Ukraine then drawing level when Roman Yaremchuk headed in from a free-kick.
Denzel Dumfries was the unlikely hero for the Netherlands with an 85th-minute winner, though De Boer was concerned at the way his team conceded twice to let slip such a commanding position.
"You know Yarmolenko is left-footed, he's famous for it. We have to defend it better, even if it was a great goal. It was not necessary," De Boer said in his post-match news conference.
"The second goal was a free-kick. Two players were too enthusiastic and that's the reason why there was no offside given.
"We have to learn from these mistakes so hopefully next time they do not happen. The opponents always get opportunities, but you hope it will not happen because of your own faults.
"These two goals, I'm sure, were not necessary."
85 - Denzel Dumfries' winning goal for the Netherlands in the 85th minute against Ukraine was their latest winning goal at the European Championships since current manager Frank de Boer scored an 89th minute penalty against the Czech Republic in a 1-0 win at EURO 2000. Timely. pic.twitter.com/Nkj3oH1ZqT— OptaJoe (@OptaJoe) June 13, 2021
All the drama came after a scoreless first 45 minutes, making it the first match in European Championship history to see five goals go in after the break having been 0-0 at half-time.
The contest followed a similar pattern to other games so far in the tournament: Euro 2020 has seen just four first-half goals compared to 15 after the interval, that second-half tally well above the 9.2 xG (expected goals) number, per Opta data.
The Netherlands have qualified for the finals for the first time since 2012, with this their first European Championship win since the 2008 edition.
"There were a few moments when we tried to counter but they could open up the game. We should be smarter on these opportunities, sometimes make a foul to stop the game," De Boer continued.
"We have to look for a better way. You cannot play 90 minutes without making a mistake, that's not realistic.
"We will have to analyse these things and see in what ways we need to improve. We have to try and not give away these dangerous moments for opponents."
Ukraine boss Andriy Shevchenko was pleased with how his players responded to the situation of finding themselves two goals down, even if their fightback eventually came to nothing.
"I think it was a quick and interesting game, loads of opportunities for both teams," he told the media.
"I want to thank my team for the reaction they showed, especially when down 2-0. We had a great reaction, found energy to change the attack and the formation. They showed themselves very well."
North Macedonia, who lost 3-1 to Austria in the earlier kick-off in the group, are next up for Ukraine.