Successful in what regard? If we are talking about economics and state building, it's highly disputed that Tito was "successful" because the Yugoslav state and economy were heavily reliant on support from the West, and the system rapidly unraveled when Western support ended. Yugoslav industries were horribly inefficient, owing to an ineffective system of collective and elected management, and pervasive corruption among the upper ranks. The economy was supported by millions of migrant workers who would travel to other European countries (most notably West Germany). Singapore, in contrast, was one of many economic success stories in the past sixty years that applied the "Kishi system" of economic management, and it hasn't unraveled because the economy was built on much stronger foundations.

Singapore, like Japan, South Korea, and later the People's Republic of China, applied an economic system derived primarily from the experience of Japan in Manchukuo between 1931 and 1945. Nobusuke Kishi, the primary economic manager for the Japanese occupation, functioned as an "entrepreneur manager", essentially directing investment into areas of his choosing, and rewarding businesses that were successful in creating large volumes of A) military-relevant output, and B) export-worthy goods, while allowing others to fail. Key to his approach was a theoretically large role of the state (though the Manchukuo economy and those that were modeled after it in the post war in practice involved less than 20% of the economy being state owned).

Lee Kwan Yew in Singapore combined this approach (which manifested in a number of state owned and state-directed investment schemes, most famously Temasek) with his own innovations, following his generally eclectic approach of drawing on multiple academic and theoretical influences. He combined this approach with a vigorous pursuit of foreign capital, aiming to provide excellent infrastructure and state services to enable Asian and European investment to flow into Singapore, which was capital poor and unable to grow its economy through domestic savings. Unlike South Korea and Japan, Singapore also lacked American aid inflows and a state budget large enough to guarantee loans on behalf of businesses, so attractiveness for foreign investors became paramount.

Ultimately, the economies of Singapore and Yugoslavia following the retirement or death of their founding leaders were worlds apart. Singapore had developed a strong export and trade based economy and had become a desirable destination for foreign investment in manufacturing and transit, while Yugoslavia was filled with perpetually-subsidized and unprofitable worker syndicates, and buoyed by millions of migrant workers who flocked to Germany. Unlike Yugoslavia, and even South Korea and Japan, Singapore had built its economy largely without politically motivated aid. Yugoslavia, meanwhile, was entirely dependent on the goodwill of the West. When this goodwill evaporated following the retreat of Soviet Communism (Yugoslavia having been valued by the West for its resistance to Moscow), the Yugoslav economy abruptly collapsed through no fault of Tito's successors.

Sources:

Petrav, Zdrako. The Political Economy Background of Yugoslav Dissolution.

Brown, Michael. The role of economic factors in social crisis: The case of Yugoslavia.

Rastin, Tayaz. Model for Development: A Case Study of Singapore’s Economic Growth.

Huff, Greg. The Economic Growth of Singapore: Trade and Development in the Twentieth Century.