Daniel Hughes urged Sussex to push on for a precious win after his big century put them in charge against Derbyshire.
The Australian opener made 144 as the hosts established a strong position after day one at Hove of their Vitality County Championship division two clash.
Derbyshire elected to bowl first then saw Hughes and Tom Haines put on 196 in just 36 overs. Haines made 72 and, after Hughes departed, Tom Alsop hit an unbeaten 69 as Sussex closed on 391-4.
It was just the response they would have wanted after losing only their second game of the season to promotion rivals Yorkshire last week.
They began the game six points clear of second-placed Middlesex and nine ahead of Yorkshire, who are playing each other at Headingley, but three of their remaining four matches are at the 1st Central County Ground where they won three out of four this season and know the conditions well.
Hughes said: "There was a little bit of swing at the start but the ball was coming on nicely.
“We got away with a few early boundaries and the best way for both of us to play is positively and by showing intent and when we walked off at lunch it was very pleasing to have put the team in such a good position.
“We wanted to start this game well because as a team in the last game [at Yorkshire] it took us a couple of days to get going and if you do that the game is pretty much gone.
“We haven't won the game yet but we have put ourselves in a good position tomorrow to go and get another couple of batting points and push on from there.
"I did think for an over or two that I might be able to score a hundred before lunch because you don't get opportunities like that very often, but they bowled pretty tightly towards the end of that session. I felt good.
“It's a nice wicket to bat on so when we go and bowl we can come up with some plans."
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