Michael O'Neill was left to rue missed chances as misfiring Northern Ireland fell to a 1-0 defeat to Finland on Sunday night.
A scrappy goal from Benjamin Kallman in the 28th minute proved the difference at Windsor Park, the close-range finish puncturing the atmosphere around O'Neil's homecoming.
It was a cruel reminder of the work ahead for returning boss O'Neill, amid a tight Euro 2024 qualifying group which saw Kazakhstan beat Denmark earlier in the day.
Read more: Northern Ireland vs Finland as it happened at Windsor Park
Dion Charles, Thursday's match hero in San Marino, was denied by the legs of Lukas Hradecky in the first half and had a goal disallowed for handball after the break.
Substitute Josh Magennis also blazed a second-half volley over the bar.
"I thought it was a tight game. We showed a lot of good sides of ourselves tonight, but we didn't take the chances we had which would have made a big difference. And we gave away a scrappy goal," O'Neill said.
"And that was the difference in the game. We felt we should have taken something away from tonight.
"But I can't fault the effort and commitment of the players, and their attitude was first class. And we are asking a lot of some very young players, and players who maybe aren't playing regularly for their clubs.
"But they gave everything tonight. Our only disappointment is we came out on the wrong side of a very tight game."
Northern Ireland's next games in Group H are in June when they travel to Denmark before hosting Kazakhstan.
It is a double-header that could determine their Euro prospects.
"Tonight is damaging because we have missed the opportunity to get points at home which is always important," O'Neill said.
"But it is not a result we can make up for. We have to make sure we win games on the road that people may think are more difficult.
"At the end of the day it is three points lost, nothing more than that. And we have to believe we can get them further down the road in the campaign.
"As the campaign progresses hopefully we will be a little bit stronger with personnel as well, and if that happens we believe we can make amends."
He added: "The results today show how tight the group can be. I didn't see the Kazakhstan vs Denmark game earlier but you see Denmark are 2-0 up and lose the game in the final 15-20 minutes.
"It is a result nobody expected, but all these games are difficult. Logistically, playing Kazakhstan away is difficult to prepare for and we have to go there on the back of playing Slovenia in game six.
"So it is a group where it might not take the points total that in the past you would need to finish second, because a lot of teams will take points off each other."
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