London Broncos booked their Challenge Cup quarter-final place after proving just too strong for part-time Batley.
The Broncos dominated early on as they moved 16-0 ahead after only 20 minutes following tries from Jamie O'Callaghan, Matt Cook and Antonio Kaufusi.
But Batley fought back bravely with Danny Maun and Mark Applegarth scoring and Gareth Moore adding two goals to reduce the deficit to four points.
Chad Randall's second-half try saw the relieved Broncos into the last eight.
This year's Challenge Cup quarter-final draw will take place on Tuesday, 1 May at 0820 BST, BBC Radio Five live.
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Batley coach John Kear said:
"I'm very proud of my part-time lads. I thought it was a manful effort.
"We wanted levelling conditions and we certainly got them. The players are absolutely frozen. You've got to compliment both sets of players because they were horrific conditions.
"As the conditions worsened, the field got heavier and opportunities became less and less.
"I was disappointed with our second-half kicking game but I think that was in part due to London's defence."
London Broncos coach Rob Powell said:
"We knew it was going to be tough. In front of that sort of crowd and against a John Kear-coached team who have got some very good and enthusiastic players, we had to dig in.
"I thought the boys were pretty impressive with some of the individual performances and the way they went about their business.
"Some of those young London blokes have only ever played at nice grounds - they've never played proper rugby league on a hill with the rain coming across sideways before - so it was a bit of an experience for them.
"They'll get some good experience out of that. Some of our Aussie guys won't have played in those conditions either."
Batley: Preece, Potts, Walton, Maun, Brown, Black, Moore, Smith, Mennell, Potter, Bretherton, Applegarth, Lythe.
Replacements: Grehan, Hirst, Walmsley, Palfrey.
London Broncos: Robertson, O'Callaghan, Channing, Sarginson, Dixon, Witt, Gower, Kaufusi, Randall, Bryant, Cook, Rodney, Bailey.
Replacements: Temata, Krasniqi, Melling, Dorn.
Referee: T Alibert (Toulouse)