Republic of Ireland striker Adam Idah made his first Champions League start as Celtic produced an impressive response to their thrashing in Dortmund by holding Atalanta to a goalless draw in Italy.Brendan Rodgers' side followed their 7-1 defeat by Borussia Dortmund by keeping their first clean sheet at this level since a 3-0 win at Anderlecht seven years ago.The Scottish champions had to withstand spells of sustained pressure with the Europa League holders registering 23 efforts at goal but Celtic had some moments of their own.The result left Celtic on four points from three matches having played their toughest two away fixtures on paper in the eight-game league format.Celtic were again missing the injured Greg Taylor and Cameron Carter-Vickers from their back four but Auston Trusty and on-loan Barcelona left-back Alex Valle delivered their best performances since joining towards the end of the transfer window, while Ireland defender Liam Scales was also excellent throughout.Reo Hatate started in midfield and gave Celtic some composure on the ball while Idah was handed a chance up front, but generally struggled to hold the ball up.Celtic were handed a suspended two-year ban on away fans since that defeat in Germany and there was no repeat of the pyrotechnic displays that would trigger the punishment, although the home supporters did let off smoke bombs and flares.Idah and Nicolas Kuhn threatened to get in behind early on but it was soon clear that the Celtic defence would be regularly tested with balls from out wide.Mario Pasalic came closest to breaking the first-half deadlock with a header off the bar before nodding the rebound over.