Klose, 32, who has 14 World Cup goals to his credit and is just one away from matching Ronaldo's all-time record, scored his 53rd goal for his country on his 102nd appearance.
"It is always a bit difficult after a World Cup, because we still don't have the match practice," said Klose, after Germany finished third in South Africa.
"We did well here, but in the first half we turned over too much possession.
"In the second-half, we acted smarter and got the goal, but at the end of the day we need to iron out our mistakes."
"It was important we came away with the three points," said Germany captain Philipp Lahm.
"We know we have 13 months of qualifiers, we have a long and hard road ahead of us."
Belgium coach Georges Leekens said he was proud of his young side.
"We had high hopes before this match, but we lost three points, although my team fought well," he said.
"The players wanted it and they created chances, but Germany are effective.
"What we saw tonight is a good basis for the future. This is not fantastic, but it was a promising game for us."
With Michael Ballack working his way back to fitness after the ankle injury which kept him out of the World Cup, Bayern Munich's Lahm captained Germany at right-back with Hamburg's Marcell Jansen on the other flank.
The Belgian side had an average age of just 24 years, four months with Lille's 19-year-old Eden Hazard on the left wing, with Germany at 25 years, one month on average as both sides look to the future.
Belgium had the better of the chances in the opening spell as Lukaku went one-on-one with goalkeeper Manuel Neuer on 11 minutes.
Kompany picked up the first yellow card when he sent Klose crashing to the turf after 12 minutes, but Bastian Schweinsteiger was wide of the mark with his free-kick.
With half-time approaching, Belgium raised the pace as first Hazard broke through the German defence, then Fulham's Moussa Dembele forced Germany goalkeeper Tim Wiese into a diving save on 38 minutes.
With Germany becoming frustrated, Schweinsteiger picked up a yellow card just before half-time after he went too high into a tackle on Belgian midfielder Jan Vertonghen.
The guests took the lead when Mueller capitalised on a mistake in the Belgian defence to thread a pass through to Klose who slotted past Belgium goalkeeper Logan Bailly on 51 minutes.
Source: AFP Global Edition