Syria had for several years cracked down on supporters inside the country of the Kurdistan Workers Party, which has waged an armed struggle for decades against the Turkish state. Erdogan was seen to be more independent of US influence than any previous Turkish leader and much more critical of Israel.
However since the beginning of unrest in Syria the countries have diverged substantially.
One factor appears to be the unwillingness of Syria's Assad government to follow the Turkish model, assumed to mean that a country should follow a pro-Western foreign policy, a free-market economic programme that favours international big business, and actively promote conservative Islam throughout public life.
President Bashar Assad rebuffed his would-be Turkish mentors as offering impractical solutions for Syrian realities. Instead he promised economic reforms and a relaxation of the country's authoritarian political system, but without falling into step with Washington.
The second factor in worsening relations is Ankara's obvious belief that it should turn its attention to influencing the forces that might dominate a post-Assad Syria.
In April, Turkey hosted the second Friends of Syria conference, a gathering of states hell-bent on regime change, and it has tried to broker unity between the egos and factions of the disparate exile opposition groups.
Both Turkey and Syria have substantial Kurdish populations and both have suffered ethnic discrimination. The Kurdish fault line is often overlooked in Western coverage of the conflict, but it is a critical element.
In Turkish Kurdistan, Erdogan's AKP party has continued the Turkish state's repression against the separatists but he has also made electoral inroads at the expense of Kurdish nationalist parties, including those acting as legal wings of the PKK.
Kurds in south-eastern Turkey are mostly Sunni Muslim by religion and socially rather than politically conservative.
The AKP's image as a party constantly at loggerheads with the army high command is also a positive factor in a region that has suffered terribly at the hands of the military.
As the country's largest minority, post-independence Syria's Kurds faced considerable persecution, with the Kurdish language banned in public and in schools although both the much smaller Assyrian and Armenian communities were allowed education in their mother tongues.
In the early 1960s, tens of thousands of Kurds had their Syrian citizenship revoked, leaving them without access to state benefits or employment.
With such a history of oppression many Kurds turned to the left, but during the period of the United Arab Republic with Egypt the Syrian Communist Party was viciously repressed too.
The Ba'athist revolution of 1963 did nothing to change the status of Kurds. The Ba'athist philosophy of pan-Arabism rarely allowed space for the expression of Kurdish identity and Kurdish nationalists were seen as little more than a fifth column of outside powers.
In recent years there have been episodic clashes between the Kurdish communities in the north of the country and Syrian government but there was little sympathy for them from their ethnic Arab compatriots and the protests failed.
President Assad has belatedly started to restore Syrian citizenship to thousands of "stateless" Kurds to bolster support for his government and has signalled the need for a new relationship between the government and this community that accounts for 10 per cent of the population.
Kurds are also being courted by the opposition.
The opposition Syrian National Council has named Abdulbaset Sieda, a Syrian Kurd living in exile in Sweden, as its new leader. But Sieda is not seen as having much grass-roots support within the Kurdish opposition. In fact, the Kurdish National Council (KNC), an umbrella organisation of around 10 anti-Assad groups, walked out of the Istanbul summit in April enraged by the Arab chauvinist attitudes of the Syrian National Council.
Abdulhakim Basar of the KNC told Reuters at the time: "If we don't reach an agreement now, these issues will be more complicated after the regime (falls).
"Maybe we are afraid of an internal war between the Syrian factions, so we prefer to reach an agreement now to avoid this.
"Syria has to be for all Syrians without discrimination."
Other Kurdish forces have kept an even greater distance from the SNC and the Free Syrian Army.
The renewed conflict between Turkey and Syria has reopened space for pro-PKK forces in Syrian Kurdistan.
Although imprisoned PKK founder Abdullah Ocalan publicly disavowed the group's nominal attachment to Marxism and the party dropped the hammer and sickle from its emblem, the PKK maintains an essentially secular pan-Kurdish nationalist force with leftist roots.
The Democratic Union Party (PYD) is the Syrian wing of the PKK and is naturally fiercely opposed to any Turkish interference and ideologically hostile to the dominant SNC Islamist group.
PYD leader Salih Muhammad stated earlier this year: "Foreign intervention in Syria will open the door for Turkey and that is only in the best interest of Muslim Brotherhood. We won't work with anyone who supports Turkish intervention in Syria."
This has already led to clashes between it and the mostly Sunni Arab Free Syrian Army, which has been blocked from operating in territory controlled by the PYD. In these circumstances, Damascus has seen the PYD as a useful buffer force.
Regardless of the obvious failings of the Assad government, the possibility of a Syrian National Council/Free Syrian Army victory promises an even more uncertain and bloody future for the country.
It certainly seems unlikely that Syrian Kurds would accept SNC overlordship. Syria's multifaith and multiethnic make-up would probably not survive even in its past imperfect form as sectarian, ethnic and ideological differences would fracture the country.