United also have three games in hand on Loxwood and United joint manager Fred Proto said: "I'm pleased because we've not been at our best since the long break and it was good to return to winning ways. The pitch was bobbly and bumpy and it was a potentially difficult game."
Julian Curnow put United ahead in the 19th minute from the penalty spot, and he then added another from the spot after Gareth Green was fouled.
Martin Rowe pulled a goal back for Steyning early in the second period but a Green header and a Wayne Joseph strike sealed the win for United.
Proto added: "They came out firing for the second half and we just had to ensure we killed the game off. It's tight up at the top but it was a good result."
United's match at Wealden on Tuesday was postponed owing to a waterlogged pitch.
UNITED: Standen; Hunt, Curnow, J.Elliot, Philpott; Green, Benn, Mitchell, Joseph; Annis, P.Elliot. Subs: Koroma (Joseph 70), Spright (Green 80).
Storrington manager Ricky Hamilton rued what he described as "missed gilt-edged, 24 carrot chances" as Swans went down 2-1 at Westfield in Division 2.
Kristian Harding missed two one-on-ones and Dave Tidman had a shot well saved before Westfield took the lead when their winger Andrew Garman cut in and shot home.
Richard Ayres levelled things on 51 minutes, but Westfield regained the lead as Danny Woodley flicked home when a half-cleared corner was put back in the box.
Hamilton said: "We started well and should have had it dead and buried after 25 minutes.
"No one could complain if we had been three or four up but we didn't take our chances and kept them in the game when they should have been well out of it.
"Once again, it was the story of our season. I just can't put my finger on why we play so well one game and not the next. One good thing was that after we went behind, we kept creating chances."
STORRINGTON: Elliott; Davis, Carter, Watton, McCall; Tidman, Ayres, Rhodie, Humphries; Harding, Grantham. Subs: Cook (Harding 70), Sleat (Tidman 80).
Lancing's poor form continued as they crashed 5-0 at title-chasing Rye.
Lancers manager Martin Gander said: "Rye were too good for us, we didn't play that badly and sometimes you just have to accept that teams are better than you on the day.
"In my opinion, they're the best side in the league and we were beaten by the better team. We defended well for the first 40 minutes but there's not much else we could have done."
Lancers kept it tight until shortly before half-time, when Luke Woodley put Rye ahead.
Danny Ellis grabbed a double to make it 3-0 and Rye added to their tally through Danny Leach and Dominic Clarke.
LANCING: Green; Ford, Early, Gander, Mighall; Boswell, O'Toole, Garnham; Shuga'a, Griffin, Clayton. Subs: Skipper (Clayton 70), Goatcher (Shuga'a 75), Rea.
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