Harry Finch's battling half-century meant Sussex just had the better of an absorbing first day in their Bob Willis Trophy encounter with hosts Middlesex at Radlett. Finch batted for more than three hours to hit 12 fours in a top score of 69 out of the visitors' total of 293 all out.

Delray Rawlins weighed in down the order with a run-a-ball 46, but Sussex's day was marred by a back injury to opener Tom Haines, who returned late in the innings with a runner, but looked in great discomfort.

For Middlesex, there were four wickets for allrounder Martin Andersson and Blake Cullen, making his debut for the county, aged 18, returned figures of 2 for 51.

The morning session was a story of a missed opportunity for England hopeful Phil Salt. The opener battled through testing overs from Tim Murtagh and Miguel Cummins, surviving a scare when he lifted the former just over the head of the latter at mid-on.

It was the cue for Salt to push on and he produced a gorgeous shot to loft left-arm spinner Thilan Walallawita back over his head for a straight six. Another maximum followed when he pulled a short one from Cullen over the square leg fence, but his good early work was undone when he attempted to hook Andersson's first-ball bouncer and only succeeded in top edging it to Cullen at fine leg to depart for 42.

It proved to be Middlesex's only success pre-lunch as fellow opener Haines steered the visitors to 80 for 1 at the interval. However, Haines hadn't added to his tally after the resumption when he propped forward to play a defensive shot against Walallawita only to suffer a back spasm. He was briefly treated on the field before heading back to the dressing-room for intensive physio.

His replacement Tom Clark struck two sweet boundaries before becoming the first first-class victim for Cullen, edging a ball which left him off the pitch to a diving John Simpson behind the stumps.

That brought Sussex skipper Ben Brown to the crease, another man who historically has flourished against Middlesex. He and Finch played nicely through much of the afternoon, each producing some sweet cover drives. They both survived scares, Brown almost turning a ball from Walallawita into the hands of short leg, while Finch drove loosely at Murtagh, the ball flying wide of the grasping hands of Sam Robson at slip.

It was something of a surprise when Brown fell to the last ball before tea, mistiming a pull at Murtagh and spooning the ball gently into the grateful hands of Robbie White at midwicket.

Finch found fluency after tea, plundering three fours from one Cummins over as he and new batsman Aaron Thomason raised the 200. However, it would all end in disappointing fashion for Finch as he fenced at a straight one from Cullen, giving Simpson the simplest of catches.

Thomason meanwhile had taken 30 balls to get off the mark, but then only made 10 before Andersson pinned him lbw.

Rawlins and Ollie Robinson stabilised matters again with a stand of 35 before Cummins returned to trap the latter lbw to one which looked a little high. If there was doubt about that Jack Carson was stone dead to the next delivery, but Mitchell Claydon survived a lifting hat-trick ball.

Rawlins cut loose with an enormous six over the old pavilion off Walallawita and three successive fours from the returning Andersson. The young allrounder gained revenge when Rawlins holed out to Nick Gubbins on the fence, but his swashbuckling effort had edged Sussex ahead of the game once more.

The limping Haines returned with a runner, but Andersson had Claydon taken at slip before Murtagh scattered Will Sheffield's stumps to end a fascinating day.