Leicester kicked off their Heineken Cup campaign with a 28-12 victory over Aironi but came up a try short of a crucial bonus point.
Tom Croft and Alesana Tuilagi crossed as the Tigers dominated the first half, but Leicester struggled after the interval and it was not until the 80th minute that Niall Morris went over for their third try.
It is 10 seasons since Leicester claimed back-to-back Heineken Cup titles and they enter their latest assault on Europe following a dismal and injury-ravaged start to their domestic campaign.
The Tigers were more than aware of the threat Aironi pose after they caused the biggest upset of last year's competition with a 28-27 victory over Biarritz.
Leicester got off to a flying start at Stadio Brianteo in Monza and surged into a 13-0 lead within 15 minutes thanks to a pair of quick-fire penalties from the boot of Flood and a try from Croft.
With Sinoti Sinoti in the sin-bin Leicester stretched the hosts either way and after working the overlap Alesana Tuilagi released Croft to squeeze in for a converted try.
The visitors continued to threaten in attack and they clinched a second try after 25 minutes when Tuilagi took a short ball off Flood and crashed over. The England fly-half dissected the posts to take the score to 20-0 but Aironi quickly hit back with a penalty.
They continued their resurgence with a second Orquera penalty on 33 minutes to bring the scores to 20-6 at the break.
Flood struck the uprights within two minutes of the restart but he made no mistake three minutes later to stretch Leicester's lead to 23-6.
Orquera quickly struck back with his third penalty and following a sustained period of pressure he slotted another on 68 minutes to make it 23-12.
That appeared to stir the Tigers to life and they should have grabbed their third try on 72 minutes but unmarked Tuilagi failed to hold onto Matt Smith's wild pass.
They continued to hammer away at the hosts but could not break Aironi's unforgiving defence until it was too late.
Following some strong carrying by Thomas Waldrom, the visitors worked the overlap and Leicester captain Geordan Murphy threw a pinpoint miss pass to fellow Irishman Morris for a touchdown in the corner.