Grigor Dimitrov needed just two more games against Alexandr Dolgopolov to seal his place in the semi-finals of the Sydney International when play was suspended due to rain on a day in which none of the four quarter-finals were completed.

Fourth seed Dimitrov fought back to lead 4-6 6-3 4-2 when the rain returned on Thursday after the weather had led to disruptions earlier in the day at the Sydney Olympic Park Tennis Centre.

World number 28 Dimitrov had as many as 15 opportunities to break Dolgopolov's serve, but took only three of them to edge in front after losing the first set.

Dolgopolov took the upper hand when his second break in the first set gave him the chance to seize the initiative, but the eighth seed made hard work of it as he saved four break points before ending Dimitrov's resistance.

Dimitrov won the only break point of the second set to level the match, then broke in a marathon third game of the third set and will resume serving with the semi-finals in touching distance at 40-30 up on Friday.

Gilles Muller won a first-set tie-break against sixth seed Jeremy Chardy 7-5 after being 5-2 down, but no further play was possible.

The quarter-final between Viktor Troicki and Nicolas Mahut was on serve at 2-2 in the first set when the rain returned, while Bernard Tomic and Teymuraz Gabashvili were unable to start their last-eight contest.

Play will resume at 10:30am local time on Friday due to the disruptions on Thursday.