Alex Carey took the game away from NewZealand.
In their contest against the defending champions on Saturday, the Kiwis restricted the Aussies at 243 but failed to overhaul the target as their entire team was bundled out for 157 runs, courtesy Mitchell Starc's 5/26. The defending champions were once reeling at 92/5 but it was Usman Khwaja's 88 and a valiant 71-run knock by wicket-keeper Alex Carey which took Australia to a fighting total.
As Aussie skipper Aaron Finch praised Carey for making the difference, Williamson also felt that the stumper's innings on a slow wicket was something which took the game away from them.
Speaking at the post-match presentation, the Kiwi skipper said: "We weren't able to break that partnership (Khwaja and Carey) and Carey came and took the game away - a brilliant innings on that surface. I think Australia adapted better than we did."
Williamson meanwhile, also felt the pitch at Lord's was difficult to bat on and said: "It was a challenging surface if you could hit the wicket hard. The nature of the slope here always brings about movement and some uneven bounce. We were in a position of strength in the first half of the first innings at 92/5. Credit to the way they rebuilt and got themselves to a competitive total."
The Kiwis will face host England in their next and last league group game of the showpiece event and another loss will make their chances of entering the knock-outs tough. Facing such a crunch situation, Williamson said he and the team management will need to read the wicket perfectly beside making the right moves.
"It's important that we move on quickly from this game. We need to do better on the next surface. We need to have a look at the surface when we get there and make the right decisions accordingly. The wickets haven't been what most people expected, and they're getting tired towards the end of the tournament," he concluded.
The Black Caps, who have 11 points from eight games and their semi-final berth is still uncertain, will be up against the hosts on July 3, while defending champions Australia, who have 14 points in their kitty, will take on South Africa in their last league affair at the Old Trafford, Manchester on July 6.