Estoy usando lo siguiente para trazar una fecha xy un decimal. Funciona muy bien sin la línea comentada (dispersión), pero si lo descomenta, muestra todo en un eje x

¿Qué me estoy perdiendo

Gracia

import matplotlib.pyplot as plt
import datetime

fig = plt.figure(facecolor="#979899")
ax = plt.gca()
ax.set_facecolor("#d1d1d1")
plt.grid(True)
plt.title("This is a title",fontsize=16)

plt.xticks([datetime.date(2018,11,20),datetime.date(2018,11,21),datetime.date(2018,11,22)],["11/20","11/21","11/22"])
plt.yticks([0.0,0.1,0.2,0.3,0.4,0.5,0.6,0.7,0.8,0.9,1.0],["0.0","0.1","0.2","0.3","0.4","0.5","0.6","0.7","0.8","0.9","1.0"])

x1 = [datetime.date(2018,11,20),datetime.date(2018,11,21),datetime.date(2018,11,22)]
y1 = [0.18,0.32,0.21]

for i,item in enumerate(y1):
    xP = x1[i]
    yP = y1[i]
    plt.text(xP,yP,str(item)+"%",fontsize=11)

#plt.scatter(x1,y1)
plt.plot(x1,y1)
plt.show()