First and foremost, this analysis was based off a streaming video, since the race is not downloaded yet [as far as I know], so some hand times were used [which has inherent errors].
Cesar Cielo 21.39 50 LCM Freestyle
Compared to his world record swim, Cielo spends more time underwater, bringing him close to the 15-m mark. This dropped his stroke count from 4 (during his world record) to 2 strokes. This propelled him to a 15-m time of 4.89-seconds, nearly two tenths faster than his world record swim. This adjustment in his start gives one of the fastest times to the 15-m mark, comparable to Brad Tandy and George Bovell (other members of the >3.0 m/s club).
15 - 25 Meters
Cesar continued this speed as he reached the halfway mark, taking 8 strokes from 15 - 25 meters, the same as his world record swim. His velocity was nearly identical as his world record swim during this portion of the race (~2.7 m/s).
25 - 35 Meters
During the next leg, Cesar took one less stroke than his world record swim. However, this was likely continued from his longer start and finishing his either stroke during the last portion directly at the end of the 25-m mark. This part had similar time and velocity as his world record swim.
35 - 50 Meters
Into the wall, Cielo took one more stroke than his world record swim (equaling his stroke count in the world record race after removing the first 15 - m). However, this portion was nearly ~.50 seconds slower than his world record swim.
Maintain current start and underwater duration, as it provided significant time improvement. Work on maintaining stroke rate (seconds/stroke) at 0.18, instead of 0.16. Consider performing maximal efforts with tempo trainer with this set tempo.