Olympiakos was made to work hard before eventually confirming its place in the final of the Greek Cup last week against Macedonian side Aris.
Cup holders Panathinaikos, in stark contrast, strolled through to the February 20 Final against another Thessalonica opponent, division two side Iraklis.
Aris tested Olympiakos all the way, as they came close to overturning their 14-point deficit from the first leg at Piraeus.
In the two-legged tie, the cumulative total from both matches determines the winner of the contest, so Aris needed to defeat the reds by 14 points or more.
Olympiakos held on to lose by just 10 points (93-83), mostly thanks to an impressive Thodoris Papaloukas proved to be the difference.
Aris showed considerable improvement in their first game with US coach David Blatt on their bench.
In the other semi final Panathinaikos defeated A2 leaders Iraklis 99-63 for their second win in as many games, in what was little more than a training session for the European champions.
Panathinaikos will start the Euroleague Top 16 and potentially the Greek Cup Final without one of its top stars, big man Mike Batiste, after he tore a calf muscle in the semi final.
He is expected to miss at least 10 days, including the opening game of the Top 16, in which Panathinaikos hosts Partizan Belgrade next week in Athens.
The injury is the third this season for the two-time Euroleague champ, who has already missed four Euroleague regular season games.
Since returning to play and before this latest injury, however, Batiste was on his game, averaging 16 points and 5 rebounds.
Worse still for Panathinaikos is that Batiste will join another veteran and two-time champ, power forward Kostas Tsartsaris, on the injured list.
Tsartsaris will miss the entire Top 16, leading to an expectation that Panathinaikos will want to sign another big man to its frontcourt.