Skipper Ryan Chatterton blasted a unbeaten century and led an Oak Flats batting masterclass against leaders Albion Park on the opening day of their clash at Geoff Shaw Oval.

Needing a win to push for a top-two finish, Oak Flats piled on 8-412 off just 79 overs, with Chatterton making an unbeaten 114.

Chatterton smashed nine boundaries and three sixes and was supported by Kieran Gray (79), Nathan Brown (71) and Rob Hill (67).

Third-placed Oak Flats began the round 12 points behind leaders Albion Park, who realistically will need a great batting day on day two just to force a draw.

In other games, Kiama are threatening to wreck Shellharbour's finals hopes after new ball bowler Josh Simpson took 4-39 on debut for Kiama.

Shellharbour were rolled for 118 with Kiama struggling at 4-39 in reply before skipper Jye Hartgerink (18 not out) and Jake Ashley (4no) stemmed the tide, scoring 23 valuable runs.

Kiama will resume at 4-62, needing another 57 for victory.

The Cavaliers will be short a batsmen if they bat in the second innings after using their substitute on day one and then having Mitch Nevins suffer a dislocated shoulder while fielding.

"Hopefully we can get the runs we need to win on first innings," Kiama's Dan Reilly said.

"Josh taking four wickets was one of the best first-grade debuts our club has had. I'm not sure we've had a bowler take five wickets on debut, so it was great start for him."

In other games, fourth-placed Kookas are well-placed to claim a vital outright win against Gerringong-Jamberoo after taking first innings points on day one.

Josh Cuthbert took 5-22 and skipper Gerard Healey 3-12 as Kookas rolled the Jets for 75, then were bowled out in the final over of the day for 176.

Former Kookas skipper Craig Bramble made an unbeaten 60 on his return to the club.

Finally, Lake Illawarra are poised for an outright win over The Rail, who were bowled out for 57.

Lakers skipper Shane Cody took 6-11 with Lakers then declaring at 7-148, with Scott Ulcigrai making 47. The Rail are 3-18 in their second dig.

Ladder (before round 13): Albion Park 143; Lake Illawarra 142; Oak Flats 131; Kookas 130; Shellharbour 119; Kiama 75; Gerringong-Jamberoo 61; The Rail 59.