Manager Neil Lennon says Celtic still face a stiff challenge from Helsingborgs as they attempt to reach the group stage of the Champions League for the first time in four years.
"A clean sheet and two away goals is more than we could have asked for," said Lennon after
Tuesday's 2-0 win.
"It's a great result for us to take into the second game.
"But there is still a lot to play for in the tie. There was enough there to worry me. They were impressive."
Celtic's 2-0 win at HJK Helsinki in the previous round was only their second away victory in European competition in their last 34 attempts.
Yet they made it consecutive away victories thanks to a second-minute volley from Kris Commons, a second-half header from Georgios Samaras and several good saves from goalkeeper Fraser Forster.
"It was a hell of a game," said Lennon. "We got off to a dream start but then we took our foot off the pedal.
"We had to rely on Fraser to make some great saves. You can see why we pursued him so vigorously.
The return leg at Celtic Park next Wednesday should be a pulsating affair, likely to be played before a large and noisy home support.
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“I think we'll possibly have to play even better next week because I'm sure Helsingborgs will have some say in the tie ”
Lennon has concerns over Joe Ledley, who was substituted after suffering a groin injury, while defender Thomas Rogne and midfielder Beram Kayal have ankle knocks.
But Victor Wanyama will be available to face Celtic's Swedish opponents following suspension.
"There is still a lot of work to do," said Lennon.
"I think we'll possibly have to play even better next week because I'm sure Helsingborgs will have some say in the tie."
Helsingborgs coach Age Hareide was defiant in defeat, hoping his players can score early in Glasgow to test Celtic's nerve.
"Celtic will think it is over, that they are ready for the group stages. That is a good thing for us," said the former Norway boss.
"Even if they say they are not, in their minds they will be thinking it is enough and they won't lose 2-0 at home.
"One goal will make them nervous. Celtic looked disturbed and nervous in the first half and gave us some chances.
"We have to go for the first goal and if we get it we will have a chance. The pressure is still on Celtic."