The BBC pundit was impressed by the Bhoys despite their Europa League elimination.
The Bhoys traveled to Italy after drawing their first leg 3-3 with the Serie A outfit at Celtic Park, a game in which Ronny Deila's side acquitted themselves brilliantly in terms of their spirit and heart.
Where Celtic went wrong in that game defensively, though, they were far more sound at the San Siro this Thursday night.
And, despite a late Fredy Guarin strike, the Hoops produced an admirable performance against Inter - especially considering the first-half sending off of defender Virgil van Dijk.
Former Queens Park Rangers and West Ham United midfielder Sinclair, meanwhile, felt Celtic were 'outstanding' on the night, heaping praise on goalkeeper Craig Gordon in particular.
Gordon made several impressive saves once again versus Mancini's Italians, more than making up for his error during the first leg.
Next up for Celtic are Aberdeen, second in the Scottish Premiership, on Sunday afternoon. Another effort like the one the Hoops produced at Inter will do them no harm come the weekend.