Southland, who last year won the title for the first time in 60 years, have performed admirably so far in the 2012 championship without New Zealand No1 amateur Vaughan McCall.
The men from the deep south have won all three of their matches to lead Division One and shape as real title contenders.
Wellington, who are the most successful team in the history of the Toro Interprovincial with 13 victories, have also made a solid start to the week at Balmacewen.
Their No1 player Marc Jennings got them home in the morning, winning 1-up at the last hole over Cameron Grant to finish off a 3-2 win over Aorangi. They backed that up with a 3-2 win over Taranaki.
Auckland, the second-most-successful team in the event with 12 wins, are having a mixed time. They were well beaten 4-1 in round three by Manawatu-Wanganui before they defeated Aorangi 3-2.
One of the pre-tournament favourites, Canterbury, kept in touch with the leaders after a 3-1 win over Poverty Bay East Coast.
Poverty Bay provided the upset so far when they defeated North Harbour 4-1 in round three.
Bay of Plenty, who have won the event six times and have been one of the most successful in the recent era, beat a confident young Northland team 3-1 in the morning before dismissing North Harbour 4-1.
The Bay are the last team to win the trophy back to back, when they achieved that feat in 2007-2008, and yesterday they made up ground on Division Two leaders Otago.
The format of the championship sees the 15 teams split into two divisions with the top two teams from each division advancing to the semifinals on Saturday with the final to be contested on Saturday afternoon.
