Only the threat of rain and a flattening pitch loomed as possible barricades for New Zealand, who closed day three on 171 for one with nine wickets in hand.
Tom Latham was on 72 with master batsman Williamson on 48.
Although Sri Lanka have their backs to the wall, forecast rain and an easy wicket meant it was crucial for New Zealand to get the timing of their declaration right, according to bowling spearhead Tim Southee.

“With the new ball, it’s important for us to try and make early inroads,” he said.
“It’s not going to come easy. If batsmen get in on this wicket there’s not too many demons in it so we’re going to have to work extremely hard to take 10 wickets.”
Williamson, who started his innings with 992 runs for the year reached 1,000 driving Rangana Herath elegantly over mid-off to the boundary.

He joins England’s Alastair Cook and Joe Root and Australians David Warner and Steve Smith as the only players to achieve the milestone in 2015 but his batting average of 94.54 is considerably superior to the other four. Brendon McCullum, with 1,164 runs in 2014, is the only other New Zealander to score 1,000 runs in a calendar year.
Williamson’s class shone as New Zealand ramped up their dominance over Sri Lanka, removing their last six wickets on Saturday to have the tourists all out for 294, 137 runs in arrears.
Guptill and Latham set about building on New Zealand’s advantage, moving swiftly to 79 before Guptill’s luck ran out when he was bowled by a shooter from Herath for 46.

The first-innings century-maker had earlier survived caught-and-bowled chances to Nuwan Pradeep and Suranga Lakmal and being dropped on 19 by Kusal Mendis at cover.
Latham, who posted his seventh Test 50 with a single off Milinda Siriwardana, has been content to build partnerships – first with Guptill then an unbroken 92-run stand with Williamson.
Sri Lanka suffered a setback at the start of the day when they resumed their first innings at 197-4 and lost batting general Dinesh Chandimal with the first ball he faced.
The Sri Lankans had expected Chandimal to lead them within close range of New Zealand’s 431, instead he was unable to add to his overnight 83 as he fell to Southee.

Southee struck again in his next over when he had Kithuruwan Vithanage caught behind for 22.
Siriwardana and Herath emerged from the setback to produce a stubborn 43-run stand for the seventh wicket.
The 30-year-old Siriwardana, who made his Test debut only two months ago, had a reprieve on 29 when he was caught by a leaping Doug Bracewell on the long-leg boundary.
The apparent dismissal turned into a six when Bracewell fell backwards over the boundary rope.
However, Siriwardana was not to score again as four balls later he edged Neil Wagner to Ross Taylor at first slip.
Herath, who weathered a sustained short-ball barrage and took a cruel blow to the head, faced 74 deliveries before he was gone for 15.
The innings ended when leg-spinner Mitchell Santner had Pradeep caught behind to give wicketkeeper BJ Watling his sixth catch of the innings.
It is the second time the South Africa-born Watling has taken six catches in an innings, one short of the Test record of seven jointly held by Pakistan’s Wasim Bari, New Zealander Ian Smith and England’s Bob Taylor.
For New Zealand, Southee took three for 71 and Wagner three for 87.

Scores

New Zealand 1st innings 431

Sri Lanka 1st innings
D. Karunaratne c Watling b Santner 84
K. Mendis c Watling b Boult 08
U. Jayasundera c Watling b Wagner 01
D. Chandimal c Guptill b Southee 83
A. Mathews c Watling b Southee 0 2
K. Vithanage c Watling b Southee 22
M. Siriwardana c Taylor b Wagner 35
R. Herath c Boult b Wagner 15
D. Chameera c Taylor b Boult 14
S. Lakmal not out 18
N. Pradeep c Watling b Santner 03
Extras (b1, lb4, nb4) 09
Total: (for 10 wickets, 117.1 overs) 294
Fall of wickets: 1-19, 2-29, 3-151, 4-156, 5-198, 6-209, 7-252, 8-273, 9-287, 10-294
Bowling: Boult 22-7-52-2, Southee 27-4-71-3, Bracewell 21-6-42-0, Wagner 25-5-87-3, Santner 21.1-8-37-2, Williamson 1-1-0-0

New Zealand 2nd innings
M. Guptill b Herath 46
T. Latham not out 72
K. Williamson not out 48
Extras (b1, nb4) 05
Total (1 wicket, 48 overs) 171
Fall of wicket: 1-79 (Guptill)
Bowling: Lakmal 9-0-26-0, Mathews 4-1-4-0, Chameera 10-0-40-0, Pradeep 9-1-29-0, Herath 8-1-39-1, Siriwardana 7-0-28-0, Jayasundera 1-0-4-0

After Ross Taylor hit a career-best 290, the highest score ever by a visiting batsman in Australia, to steer New Zealand to a first innings lead, Steve Smith and Adam Voges posted twin centuries to help the home side recover after a shaky start.

At the close, Australia were 258 for two in their second innings, with Smith on 131 and Voges on 101, for an overall lead of 193.

It was Smith’s 12th century and fifth this year, but his first in a second innings, while for 36-year-old Voges it was just his second hundred and came in his first Test on his home ground.

Voges reached his century from the penultimate over of the day.

Smith was dropped on 96 when wicketkeeper BJ Watling put down a tough chance down leg-side off paceman Matt Henry.

Although the match appeared set to be a draw on a lifeless wicket which has offered little assistance to the bowlers over the first four days, Australia will hope to declare on the final day and dismiss the Kiwis cheaply.

Voges wasn’t giving much away about the final day’s plan, noting the flat nature of the wicket.

“I don’t think we will do them any favours,” he said.

“Ultimately that will be Steve’s decision but the good thing is we have some options.”

Taylor said he expected Australians to set the Kiwis a target.

“The odd ball’s doing a little bit to put the batter a little bit on edge,” he said.

“But knowing Australia, I’m sure they’ll come out tomorrow and try to score some quick runs and put us under pressure.

“I’m sure whatever they give us, we’ll definitely have a go, and we’ll wait and see what happens. ”

Australia already lead the three-Test series 1-0 after beating New Zealand by 208 runs at the Gabba.

In reply to Australia’s imposing 559 for nine declared after winning the toss, the Kiwis were dismissed for 624 just before lunch, their highest total against their trans-Tasman rivals on the back of Taylor’s mammoth knock and 166 from Kane Williamson.

That made it a record combined first innings total for a Test at the WACA Ground.

Kiwi hopes were then raised when Australian openers Joe Burns (0) and David Warner (24) fell early, leaving the home side precariously placed at 46 for two, with the injured Usman Khawaja (hamstring) not taking his place at number three.

The Kiwis were still 19 runs ahead at that stage, but Smith and Voges then added 212 runs for the third wicket.

Taylor was the last man to fall in the New Zealand innings as he attempted to join captain Brendon McCullum (302 v India) as only the second Kiwi to reach a triple century in Test cricket.

However, on 290 the right-hander holed out to substitute fielder Jonathan Wells off spinner Nathan Lyon to end a 37-run 10th-wicket stand with Trent Boult (23 not out).

Former skipper Taylor passed several milestones in his innings, which was his first century since November last year, and ended a form slump that even he admitted was starting to worry him.

He broke through 5,000 Test runs and posted the highest-ever score by a visiting player in a Test in Australia, as well as becoming the first Kiwi to pass 200 against Australia.

His innings, beating the 287 of England’s Reg ‘Tip’ Foster at the Sydney Cricket Ground in 1903, was the third-highest ever for New Zealand at Test level.

Taylor, who put on 265 for the third wicket with Williamson, faced 374 balls and hit 43 boundaries in 567 minutes at the crease. Number 10 Southee gave the Kiwis a lead which seemed impossible on the opening day when he turned Mitchell Starc off his pads for four as they became the first visiting side to reach 600 in Australia since 2011. Starc was the best of the Australian bowlers and finished with four for 119.

AFP