Having celebrated 30 years in management this week, QPR boss Harry Redknapp watched on as Kranjcar came within millimetres of toasting to his boss's milestone in style.
The Croatia international allowed a dropping ball to bounce over his shoulder, before unleashing a 25-yard volley which crashed off goalkeeper David Forde's crossbar.
The 29-year-old would not dwell on the disappointment for long, though, playing a neat one-two with Joey Barton before smashing past Forde from 20 yards to open the scoring.
The Lions responded well to the deficit and should have provided an immediate rispote, only for Liam Trotter's close-range header to cannon into the side netting.
Steve Lomas's men go into the interval knowing of the sizeable task awaiting his team in the second half, with the R's defence boasting 800 minutes without conceding a goal following the opening 45 minutes.