We present a lattice QCD calculation of the $Delta I=1/2$, $Ktopipi$ decay amplitude $A_0$ and $varepsilon$, the measure of direct CP-violation in $Ktopipi$ decay, improving our 2015 calculation of these quantities. Both calculations were performed with physical kinematics on a $32^3times 64$ lattice with an inverse lattice spacing of $a^{-1}=1.3784(68)$ GeV. However, the current calculation includes nearly four times the statistics and numerous technical improvements allowing us to more reliably isolate the $pipi$ ground-state and more accurately relate the lattice operators to those defined in the Standard Model. We find ${rm Re}(A_0)=2.99(0.32)(0.59)times 10^{-7}$ GeV and ${rm Im}(A_0)=-6.98(0.62)(1.44)times 10^{-11}$ GeV, where the errors are statistical and systematic, respectively. The former agrees well with the experimental result ${rm Re}(A_0)=3.3201(18)times 10^{-7}$ GeV. These results for $A_0$ can be combined with our earlier lattice calculation of $A_2$ to obtain ${rm Re}(varepsilon/varepsilon)=21.7(2.6)(6.2)(5.0) times 10^{-4}$, where the third error represents omitted isospin breaking effects, and Re$(A_0)$/Re$(A_2) = 19.9(2.3)(4.4)$. The first agrees well with the experimental result of ${rm Re}(varepsilon/varepsilon)=16.6(2.3)times 10^{-4}$. A comparison of the second with the observed ratio Re$(A_0)/$Re$(A_2) = 22.45(6)$, demonstrates the Standard Model origin of this $Delta I = 1/2$ rule enhancement.
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