There were 7 seeds in the bottom quartile who progressed to the third round:
DrHayWyre (242, µ=0.36) over cha-shu (15, µ=1.91)
BobKrier (232, µ=0.45) over yzx (25, µ=1.62)
Andrew D Marr (218) over JoMa (39)
RobGlass (209) over java sparrow (48)
Hampuse (204) over Emeric (53)
wyxxyr (203) over yed (54)
0rpheon (197) over Sums (60)
Of those above, two made it into the fourth round. Those wins plus two more that may not be big upsets (or upsets at all) based on current µ values:
DrHayWyre (242, µ=0.36) over Avin (114, µ=0.76)
wyxxyr (203, µ=0.45) over Cardinal87 (75, µ=1.23)
PerryGreen (159, µ=1.71) over Geronimoo (31, µ=1.49)
Psyduck (135, µ=1.77) over sangatsu (7, µ=1.92)
The fourth round saw a couple notable upsets, including the aforementioned win by LazyDog. It's getting increasingly difficult to classify some of these as upsets. For example, while funkdoc was seeded higher than DG, and is still higher on the leaderboard, DG actually has a higher µ (1.99 to 1.71). By contrast, breppert is currently 5th on the leaderboard with a µ of 2.14, while LazyDog is ranked ~200 with a µ of 1.18.
singletee (57, µ=1.57) over drsteelhammer (8, µ=2.17)
LazyDog (81, µ=1.18) over breppert (17, µ=2.14)
DG (52, µ=1.99) over funkdoc (13, µ=1.71)
JW (85, µ=2.16) over Horist (21, µ=1.81)
The fifth round (still in progress), sees another win by LazyDog (!) and the takedown of the top overall seed by Seprix.
LazyDog (81, µ=1.18) over vsiewnar (16, µ=2.02)
Seprix (33, µ=1.78) over Mic Qsenoch (1, µ=2.68)
* µ values as of the time of this post.