The battle between the opposing new ball pairs was always likely to be a factor in the New Zealand-England test series.
Even so, the extent of that rivalry has probably been a surprise.
Consider that Trent Boult and Tim Southee have taken all 10 wickets in the first innings of both tests in the series, and they have all three in England's second innings of the second test, too.
Jimmy Anderson and Stuart Broad took all 10 in New Zealand's first innings at Hagley Oval, Broad's six for 54 yesterday being his 16th five-wicket haul. Only five times in test history have four bowlers shared the first 20 wickets in a test.
How New Zealand's batsmen stand up against Anderson and Broad in their second innings, probably starting today, will likely decide the outcome of the test, and the series.
New Zealand keeper BJ Watling didn't believe the new ball was as helpful in England's second innings yesterday, compared with the first.
"The pitch is definitely a lot flatter than the last couple of days," he said. "The boys didn't quite get it to swing as much as the first innings."
If Anderson, England's all-time top test wicket-taker, and Broad, No 2 on that list, have similar issues in New Zealand's second innings, the hosts likely won't be concerned one bit.
New Zealand are bidding for their first series victory since 1999. Negating Anderson and Broad over the remaining two days will go a long way to securing that ambition.