Wales had seemed to be on course for a record score as they raced in to a 22-0 lead after 17 minutes, only for the Warren Gatland's side to take the foot off the gas.
Wales were far too sloppy after that and conceded too much possession at the breakdown - with Namibia able to come back into the game when they looked down and out.
As it was, the quality and strength of the Wales squad told, though, with Scott Williams (3), Aled Brew, Toby Faletau, Gethin Jenkins, George North (2), Jonathan Davies, Lloyd Williams, Lee Byrne and Alun Wyn Jones scoring tries and Stephen Jones adding 15 points, while Rhys Priestland slotted over three conversions.
Namibia battled bravely after their woeful start but the effects of having to play four matches in 17 days clearly told on the minnows as they missed 41 tackles.
Heinz Koll did scored his second try of the tournament, while Theuns Kotze converted to ensure they avoided a second successive whitewash following their 87-0 defeat to South Africa.
Jones had marked his return to the Wales side with a successful shot at goal after just two minutes, although he was off target with his conversion attempt after Williams had raced in for his first try. Williams, making his first start for Wales, profited after a superb break from Leigh Halfpenny.
A superb offload from Bradley Davies put Brew in for Wales' second try after Namibia were guilty of conceding possession, with Jones slotting over the conversion.
It was 22-0 after 17 minutes as Faletau crashed through some weak defending and Jones converted - with Namibia again their own worst enemy after Eugene Jantjies had his box kick charged down to give Wales the attacking platform.
To their credit, though, Namibia regrouped brilliantly and began to get a foothold in the game - with the pack able to disrupt Wales at the scrum and the breakdown.
Unfortunately Theuns Kotze missed with two long-range shots at goal as Namibia attempted to get onto the scoreboard.
Having held Wales after that opening onslaught, Namibia started the second half with renewed vigour as Jantjies and Kotze looked to pin their rivals back in their own 22.
However Wales were able to counterattack and after a series of drives at the Namibians line Williams was able to wriggle through to score his second try. Jones tagged on the extras.
The try of the night came from Jenkins on 50 minutes, with the prop breaking through two tackles before holding off three more would be defenders to crash over the line. Jones converted.
If Jenkins scored the best try, the biggest cheer came as Koll scored in the corner. Nico Esterhuyse intercepted Jones' pass and offloaded brilliantly to Koll, who outstripped the defence to score. Kotze converted.
However Namibia's task was made so much harder when Raoul Larson was sin-binned.
And Wales took advantages as replacement winger North and centre Davies scored in quick succession. Jones converted both to bring up the half-century.
North was in for a second on 65 minutes after a stunning break and offload from Byrne. Priestland converted.
Even the return of Larson couldn't close the floodgates, with Williams stepping through some tired defending to complete his hat-trick. Priestland added the extras.
Replacement No.9 Lloyd Williams then got in on the act with five minutes left after a 5m scrum, while Byrne finished off a free-flowing move as Namibia looked out on their feet.
And Wales finished with their 12th try of the night - and ninth of the second half - when Alun Wyn Jones dived over. Priestland converted.
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