Both Williams drivers had a clean lap in Q1, with Pastor finishing fourth quickest, but both struggled with traffic on their final runs in Q2 which cost them time.
Valtteri Bottas: "...we saw some interesting results and noticeable differences in the way the car performed."
Williams team completed Friday's objectives.
Both drivers had a solid start and drove a good race with a lot of midfield battles taking place.
There is still work to do ahead of tomorrow for Williams team to improve overall pace and consistency.
Tropical Storm DANAS is currently heading towards Japan and is expected to skirt the coastline over the next few days.
Valtteri Bottas qualified 17th with Pastor Maldonado 18th for tomorrow's Korean Grand Prix.
Pastor Maldonado: "Our performance wasn't up to the level we hoped for today, but hopefully we can analyse the data tonight and improve for tomorrow."
First time for Bottas at the Korean International Circuit
Valtteri had a clutch problem at the start and debris in his front wing which compromised the performance of his car throughout the race.
Both drivers went out on the supersoft tyre for their second runs in Q1, with Pastor unable to progress into Q2.
Valtteri Bottas: "We need to work hard tonight to improve for tomorrow."
Both Williams drivers had a consistent race but unfortunately there wasn't enough pace in the car to challenge the top ten.
Both drivers went out on the medium tyres in Q1 to set a time, with Valtteri just missing out on Q2 by two tenths of a second.
Infiniti Red Bull Racing leads constructors’ championship with 312 points to Mercedes’ 235. Lotus F1 Team sits fourth with 187.