They had Sri Lanka 50 for five at Galle in the first test, and 12 for three early in their first innings at Colombo in the second test. Boult had the then world No 1 batsman Kumar Sangakkara out in Galle, and after putting Sri Lanka's captain, Mahela Jayawardene, through a testing examination, had him caught at gully late on Monday night.
In his 35th first-class game, Boult had taken 101 wickets as play began last night.
ND coach Grant Bradburn is delighted with Boult's development.
"I'm really impressed with the way he's bowling. It looks like he's found confidence and his feet at international level, which takes some time. He's very assured of what he's doing, has a very good understanding of his skill and what his weapons are, and he's reaping the reward of the work he's put in."
Bradburn remembers the grim times surrounding Boult's "scary" back injury.
"What it did was give him a real appreciation of what international cricket as a fast bowler requires.
"He's learnt to be so much more personally accountable with his training and his own game. He's always had the skills, no doubt about that, and he's really starting to flourish."
Bradburn said, given international workloads these days, that New Zealand needed a stable of fast-medium bowlers it could rely on. Bradburn, a former test allrounder in the early 1990s, likened them to racehorses.
"They need a spell now and again and building up, targeting certain races. It's not that different for these guys."
Boult's figures should have improved in the morning session yesterday but captain Ross Taylor dropped opener Thuranga Paranavitana at first slip on 32.
Tim Southee nabbed two wickets late in the first session.
The home side began day three at 43-3 in reply to New Zealand's first-innings total of 412 and edged past 100 before Southee struck twice in quick time.
Southee dislodged opener Paranavitana for 40, when he was caught behind by Kruger van Wyk. Angelo Mathews was next to go for 47 as Martin Guptill produced a stunning one-handed catch in the slips to give Southee his fourth scalp of the innings.
Sri Lanka closed the session at 107-5 with Thilan Samaraweera and Jayawardene unbeaten at the crease.
The home side need another 106 runs to avoid the follow-on.
Southee, who has been in good form recently after he took 4-46 in the first innings of the first test last week, went to lunch with figures of 4-35 next to his name.
- additional reporting APNZ
