Worthing insist they are still in the London Two South driving seat, despite defeat at Gosport and Fareham.
The Hampshire side kept a second successive cleansheet as they won a promotion four-pointer 15-0.
Boosted by several players from the services, Gosport scored three tries, the third coming while Worthing flanker Jodie Levett was in the sin bin.
Worthing's second defeat of the season leaves them needing to win at home to Maidstone next Saturday to keep their bid for a second successive title on course.
Coach Ian Davies said: "We didn't perform badly but I thought Gosport wanted it a bit more than we did.
"We didn't take our chances. We missed three kicks at goal which made a difference but they have got the second best defensive record in the league and they showed why."
A bruising battle saw Worthing centre Steve Imrie leave the action after 15 minutes with a dead leg and utility back Alistair Coombe suffer a facial injury.
Worthing must now do without powerful centre Adam Holloway, who is looking to further his rugby development in New Zealand.
Davies admitted: "How we react will be important. We are still there at the top but we need to re-group.
"There are some very important games coming up in this division and the good thing for us is that Gosport have still got to play Tunbridge Wells twice."
Worthing still have to play at home to Tunbridge Wells and Davies also sees home and away fixtures with Portsmouth as particularly challenging.
He added: "Nothing has changed with this defeat. We still need to win every game."
Haywards Heath also have a big game to look forward to as they host London One leaders Southend.
Heath's trip to London Nigerians was called off on Saturday.
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