Hereford climbed to their highest position, seventh, in the Vauxhall Conference since the end of September after this win at Edgar Street on Saturday.
Veteran striker Tony Agana came on as substitute for James McCue at the start of the second half to settle the issue with a 52nd-minute goal. Right-back Ian Rodgerson threaded a through ball to Agana who held off an attempted challenge before placing his shot wide of keeper Ray Newland into the corner of the net for his fourth goal of the campaign.
Injuries have limited Agana to eight appearances this season and on Saturday he was returning to action after being sidelined with a hamstring problem.
Agana said: ''You have to take your chances as they come. It was a great ball from Ian. I'm glad to have scored on my return.''
Leek have won only one away match in all competitions this term and their manager Peter Ward said: ''We did well to reach half-time on level terms but Agana showed a bit of class and we were punished by it.''
United director of football Graham Turner, pleased the Bulls had stretched their unbeaten Conference run at Edgar Street to six matches, said: ''We got a good 45 minutes from Agana but there were other saisfactory individual performances as well.
''As in the previous match when we beat Morecambe 1-0, the players deserved to have won by a bigger margin. But when we got the ball in wide positions we tended to over elaborate.''
Despite having by far the bulk of the first half play, Newland had a comfortable time in Leek's goal and was beaten only once. A near post header by Trevor Matthewson from Brian McGorry's corner eluded him but Dale Hawtin was handily placed to clear off the line.
Within a minute of the second period, however, Newland just managed to save an angled drive from Agana with his legs before the striker beat him with the match- winner.
The keeper also used his legs to keep out a drive from Chris Hargreaves from a similar position, while the midfielder headed wide after a good right-wing move between Rodgerson and Jamie Pitman.
Agana's strength and ability to hold up the ball frequently gave Leek problems and he set up a good chance for Gary Cook but the substitute fired straight at Newland.
Despite United's dominance, there was always a chance Leek might break away and snatch a point. It could well have come if Dean Trott's direction had not been awry when he met Steve Soley's cross with a diving header.
Hereford: Quy, Rodgerson, Walker, Matthewson, Fishlock, Pitman, McGorry, Mahon, Hargreaves, Leadbeater (Cook 77 min), McCue (Agana 46 min). Sub not used: Warner.
Attendance: 1,712.
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